Thanks to Kenn D. M&#248;ller and Claus Sternberg (DTU) for technical assistance and to Tue S. J&#248;rgensen for quantitative PCR analysis.

NOTE: An overview of the circular DNA purification and sequencing method (Circle-Seq) is illustrated in Figure 1.
1. Cultivation, Cell Harvest and Plasma Membrane Disruption
<ol>
	<li>Inoculate yeast cells (for example&#160;Saccharomyces cerevisiae) from an O/N culture into 50 ml complete nutrient medium of yeast peptone dextrose (YPD). Inoculate at a low initial cell density of 1-3 x 105 cells/ml or an optical density of approximately 0.01 OD600.
	<ol>
		<li>Incubate the cells at 30&#176;C with agitation at 150 rounds per minutes (rpm) until cells reach maximum cell density of approximately 1 x 1010 cells, approximately after 24 to 48 hr or a optical density at OD600 &#62; 10.0. 
		NOTE: The cultivation time is not crucial as lower cell concentrations can be used.</li>
	</ol>
	</li>
	<li>Transfer the outgrown culture to a 50 ml conical tube, pellet the cells by centrifugation at 800 x g for 3 min&#160;and discard the supernatant.</li>
	<li>Wash the pellet with 25 ml buffer solution of 10 mM Tris-Cl, 1 mM EDTA, pH 8.0, re-pellet the cells by centrifugation at 800 x g for 3 min and discard the supernatant.</li>
	<li>Resuspend the cell pellet in 1.2 ml resuspension buffer supplied from a plasmid column-purification kit.</li>
	<li>Optional step: Add highly diluted plasmids as controls for purification of circular DNA elements20. 
	NOTE: In the current dataset, a 7.7 &#181;l plasmid mixture was applied for each sample containing 1010 cells. The plasmid stock mixture consisted of three plasmids in different concentrations; pBR322 at 38 ng/sample, pUC19 at 0.5 ng/sample, and pUG72 at 0.01 ng/sample.</li>
	<li>Transfer the cell suspension into two 2 ml micro-centrifuge tubes, each supplemented with 0.5 mm glass beads at a 1:3 ratio of the total suspension volume.</li>
	<li>Vortex each tube at maximum speed for 10 min to disrupt plasma cell membranes. Pellet the beads by centrifugation at 268 x g for 30 sec&#160;and transfer the 1.2 ml combined supernatant from the two microcentrifuge tubes to a new tube. 
	NOTE: Alternative to step 1.6-1.7, use zymolyase to disrupt cells in 0.6 ml resuspension buffer solution. Ten units of zymolyase can disrupt 5 x 107 cells within 1.5 hr at 35&#176;C.</li>
</ol>
2. EccDNA Enrichment by Column Chromatography
<ol>
	<li>Follow the protocol from a kit for column purification of plasmids. In brief, treat each sample with 1.2 ml alkaline solution, mix gently and incubate 3 min at RT.</li>
	<li>Add 1.2 ml neutralization buffer, mix gently and centrifuge at 9650 x g for 5 min.</li>
	<li>Load the solution onto a column equilibrated with 1 ml equilibration solution and allow the liquid to flow through the column by gravity.</li>
	<li>Wash the column with 4 ml washing solution. When the solution has passed through the resin, carefully add 0.3 ml elution solution to replace most of the 0.35 ml column void volume.</li>
	<li>Elute DNA into a new collection tube with 1 ml elution solution and precipitate the DNA by adding 0.8 ml precipitation mixture. Centrifuge at 9650 x g for 10 min.</li>
	<li>Wash the DNA pellet with 0.5 ml 70% ethanol, centrifuge at 9650 x g for 5 min, air dry for 5 to 15 min and dissolve the purified DNA in 25 &#181;l sterile water. 
	NOTE: Only short term storage of DNA in water is recommended. Preferentially, proceed directly to step 3.</li>
</ol>
3. Digestion of Remaining Linear Chromosomal DNA
<ol>
	<li>Optional step: To facilitate specific digestion of linear DNA by exonuclease, treat the purified DNA with a rare-cutting endonuclease such as NotI. For 5 &#181;g DNA, use 1 unit NotI, 5 &#181;l 10x digestion buffer and sterile water to a total volume of 50 &#181;l. Incubate the reaction at 37&#176;C for 16 hr and heat inactivate the endonuclease at 80&#176;C for 5 min.</li>
	<li>Add 20 units exonuclease (2 &#181;l), 4 &#181;l ATP (25 mM), 34 &#181;l sterile water and 10 &#181;l 10x reaction buffer directly to the 50 &#181;l endonuclease-cleaved DNA to reach a 1x reaction volume of 100 &#181;l, using the ATP-dependent exonuclease kit.</li>
	<li>Perform hydrolysis of linear single-stranded and double-stranded DNA at 37&#176;C for 5 days or more. Add an additional 4 &#181;l ATP (25 mM), 0.6 &#181;l 10x reaction buffer and 20 units exonuclease every 24 hr to continue the enzymatic DNA digestion at a 1x reaction volume.</li>
	<li>After removal of linear DNA, sample 2 &#181;l from the exonuclease treated solution to confirm elimination of chromosomal linear DNA by quantitative polymerase chain reaction (qPCR), using a chromosomal marker such as the actin gene ACT120.
	<ol>
		<li>Each 20 &#181;l qPCR reaction volume contains 2 &#181;l exonuclease-treated sample, 150 nM ACT1 primers 5&#39;-TCCGTCTGGATTGGTGGTTCTA-3&#39; and 5&#39;-TGGACCACTTTCGTCGTATTC-3&#39;, 2% (volume/volume) dimethyl sulfoxide, and 10 &#181;l green fluorescent master mix.</li>
		<li>Use the reaction condition; 3 min at 95&#176;C, followed by 45 cycles of 15 sec at 95&#176;C and 30 sec at 60&#176;C. 
		NOTE: ACT1 is a particularly suitable marker for linear DNA since copy number variations in this gene are deleterious21-23 so eccDNA should not carry ACT1.</li>
		<li>Alternatives to analysis of DNA digestion by qPCR are&#160;standard PCR (4.3) or propidium iodide staining (4.4).
		<ol>
			<li>Use 2 &#181;l exonuclease-treated sample as PCR template with ACT1 primers 5&#39;-TGGATTCTGGTATGTTCTAGC-3&#39; and 5&#39;-GAACGACGTGAGTAACACC-3&#39;. As positive ACT1 control, use 50-100 ng genomic S. cerevisiae DNA as template. PCR reaction conditions; 3 min at 95&#176;C, followed by 35 cycles of 30 sec at 95&#176;C, 30 sec at 56&#176;C and 1 min at 72&#176;C.</li>
			<li>Run PCR reactions by gel electrophoresis on 1% agarose with 0.5 &#181;g/ml ethidium bromide. Look for a 0.8 kb&#160;ACT1 band.&#160;</li>
		</ol>
		</li>
		<li>The absence or presence of linear DNA can also be examined by propidium iodide staining before and after DNA amplification.&#8203;
		<ol>
			<li>Mix each DNA sample in a 1:1 volume with a 1:1,000 H2O-diluted solution of 20 mM propidium iodide stock. Leave solution in darkness for 10-20 min&#160;at RT and analyze DNA staining by fluorescence microscopy at 100x magnification using a red excitation fluorescence filter at 663-738 nm and an exposure-time of 5 to 30 sec. As DNA-staining control, use &#248;29-amplified genomic DNA from yeast and/or &#248;29-amplified plasmid.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Heat inactivate the exonuclease solution at 70&#176;C for 30 min.</li>
</ol>
4. DNA Amplification
<ol>
	<li>Amplify the purified and enriched eccDNA from step 3.5) with &#248;29 DNA polymerase24-26 according to the protocol of the polymerase manufacturer.
	<ol>
		<li>In brief, mix 5 &#181;l enriched eccDNA with 5 &#181;l denaturation&#160;buffer.</li>
		<li>After 3 min at RT, add 10 &#181;l neutralization buffer. Mix gently and add 30 &#181;l master mix containing 29 &#181;l reaction buffer and 1 &#181;l &#248;29 DNA polymerase. Incubate the reaction at 30&#176;C for 16 hr or more (up to 72 hr). Heat inactivate the &#248;29 DNA polymerase at 65&#176;C for 3 min.</li>
	</ol>
	</li>
</ol>
5. Sequencing and Data Analysis
<ol>
	<li>Shear the amplified eccDNA with a focused ultrasonicator to an average target peak size of 300 bp. Use the following settings for a 130 &#181;l DNA sample: 450W peak intensity power, 60 sec treatment, 30% duty factor, 200 cycles per burst, temperature 7&#176;C.</li>
	<li>Add barcode index labels and adapters to the fragmented reads for synthesis of libraries for sequencing, using an appropriate method for library preparation.</li>
	<li>Run deep&#160;sequencing, for example as 141-nucleotide single-end reads on a high-throughput sequencing platform.</li>
	<li>Map reads to the yeast reference genome under investigation and allow reads to map to multiple regions. For example, use a freely available workflow system27,28 and short-read aligner mapping software29.</li>
	<li>Identify reads from regions of putative eccDNAs using contiguous reads, for example, more than seven contiguous reads (&#62;1 kb) without gaps20. 
	NOTE: Software is available27,28 for exploring mapped reads at genomic regions of interest.</li>
</ol>

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H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+structure+of+double-minute+chromosomes+bearing+amplified+copies+of+the+epidermal+growth+factor+receptor+gene+in+gliomas.">Molecular structure of double-minute chromosomes bearing amplified copies of the epidermal growth factor receptor gene in gliomas.</a> Proceedings of the National Academy of Sciences of the United States of America. 101 (31), 11368-11373 (2004).</li><li>Ahn, K., Gotay, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+rate+of+disease-related+copy+number+variations+in+childhood+onset+schizophrenia.">High rate of disease-related copy number variations in childhood onset schizophrenia.</a> Molecular psychiatry. 19 (5), 568-572 (2013).</li><li>Girirajan, S., Johnson, R. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+increases+in+both+common+and+rare+copy+number+load+associated+with+autism.">Global increases in both common and rare copy number load associated with autism.</a> Human molecular genetics. 22 (14), 2870-2880 (2013).</li><li>Vogt, N., Gibaud, A., Lemoine, F., de la Grange, P., Debatisse, M., Malfoy, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amplicon+rearrangements+during+the+extrachromosomal+and+intrachromosomal+amplification+process+in+a+glioma.">Amplicon rearrangements during the extrachromosomal and intrachromosomal amplification process in a glioma.</a> Nucleic Acids Research. , (2014).</li></ol>

The authors declare that they have no competing financial interests.

The Circle-Seq method allows genome-scale detection of eccDNA from yeast cells with sequence-level resolution. The method is a mild eccDNA purification that does not require intensive vortex or pipetting and uses column separation by gravity to limit eccDNA breakage that would lead to exonuclease digestion in the&#160;subsequent step. These features of the method may be crucial for detecting large eccDNAs that contain gene sequences. Circle-Seq detected numerous eccDNAs including full genes (Dataset 1). It also detected the 86-kb yeast mitochondrial DNA. Thus, this protocol&#160;facilitates purification of large circular DNA elements. Keeping the number of DNA extraction steps to a minimum reduces&#160;the risk of eccDNA loss and maximizes&#160;yield. Based on results for control, spiked-in plasmids, Circle-Seq is highly sensitive, detecting a single circular DNA from 2,500 cells. Furthermore, removing abundant endogenous plasmids such as 2&#181; plasmid or mitochondrial DNA might&#160;significantly enhance sensitivity. Curing&#160;of 2&#181; from yeast cultures has been described30. Alternatively, 2&#181; and mitochondrial DNA removal might be achieved with a rare-cutting endonuclease, such as SwaI. However, the restriction enzyme step could target other eccDNAs of interest and limit the total eccDNA yield.
Critical steps for eccDNA detection were removal of linear DNA (step 3) and DNA sequencing (step 5) to a proper depth. To record the majority of eccDNAs from a cell population, deep&#160;sequencing might be required20. Paired-end sequencing should provide&#160;even greater confidence of eccDNA detection, as circular DNA junctions are expected to&#160;yield paired-end reads that map discordantly. These discrepancies support the discovery of circular DNA structures and can potentially be used as an additional eccDNA-detection filter.
The Circle-Seq method was validated using three independent S. cerevisiae CEN.PK populations. Detected sequences included previously reported eccDNAs, endogenous plasmids and spiked-in plasmids and hundreds of putative eccDNAs (Dataset 1). These findings support previous Circle-Seq datasets from S. cerevisiae S288c20. The discovery of several eccDNAs common to CEN.PK and S288c populations indicates that these loci have a propensity to exist as circular elements (Figure 4). We have previously shown that the [GAP1circle] is enriched under nitrogen limited conditions in the CEN.PK background8, though evidence of [GAP1circle] in other strain backgrounds has not been found. Finding of&#160;eccDNA from the CUP1-1 RSC30, ASP3-1, COS111, and HXT6 HXT7 loci in both S288c and CEN.PK suggests that a predisposition for DNA circularization is conserved between the yeast strains. It remains to be shown if [HXT6/7circle],&#160;[ASP3-1circle], [COS111circle], and [CUP1-1 RSC30circle] confer selective advantages to&#160;cells&#160;or if their existence is merely an effect of high rates of DNA circularization.
Taken together, the results indicate that Circle-Seq is well suited for detecting kilobase-sized eccDNAs and has advantages for identifying eccDNAs with complete genes. Circle-Seq is a highly sensitive method that enables whole genome-scale screens of eccDNAs from yeast. The Circle-Seq method could open a new field of research aimed at elucidating the role of eccDNA in generating gene deletions and amplifications. Given that DNA architecture and structure are largely conserved from eukaryotic yeast to higher eukaryotes, the Circle-Seq method should, in principle, be applicable to all eukaryotic cells, with slight modifications. At present, the method does not appear to have any limitations, although its ability to purify megabase-sized eccDNAs has yet to be shown. In addition, the use of &#248;29 DNA polymerase, which uses a rolling-circle amplification method31, creates a bias towards smaller eccDNAs making eccDNA quantification more difficult. Circle-Seq detects eccDNAs large enough to carry full genes, making it suitable for studies on double minutes&#8212;circular DNA from human somatic cells. Double minutes can contribute to cancer when proto-oncogenes are amplified on these elements32-37. Studies of eccDNAs in germline cells could be used to measure germline mutation rates and assess sperm quality, for example in livestock. Thus, Circle-Seq has the potential to yield insights into the rate at which genetic variation arises in the form of copy number variation, and lead to a novel understanding of diseases that involve gene copy-number variation38-40.

Detecting early or transient chromosomal amplification is difficult because it requires identifying alterations in single DNA molecules in large populations of cells. Chromosomal copy-number variations (CNVs) are generally detected well after their establishment, leaving only the final CNV structure as evidence of the mechanism that generated the variation1,2. Detecting and recovering extrachromosomal circular DNA (eccDNA) in earlier stages of CNV formation might elucidate ongoing processes in genomic rearrangements.
Previously, de novo discovery of eccDNA was by electron micrographs3, Giemsa staining of metaphase chromosomes4, or two-dimensional gel electrophoresis5. These methods provide little or no information about the sequence of the circular DNA. Targeted techniques such as Southern blotting6,7, inverse PCR8, or fluorescence in situ hybridization9 provide evidence only about specific eccDNA elements. None of these methods provide the sequence of all existing eccDNA types in a cell population.
Genomic divergence in a pool of cells can be characterized by genome sequencing and/or tiling arrays10,11. Detecting a deletion or amplification by conventional DNA purification methods usually requires that a mutated allele represent at least 0.1-1% of the cell population12,13. Acentric eccDNAs are expected to be even more transient in a cell culture due to their lack of centromeres and potential absence of DNA synthesis at replication. Thus, since most eccDNAs presumably are in low amounts and their sequences resemble the genome, alternative DNA extraction methods are needed to detect eccDNAs.
Several circular DNA purification techniques exploit the structural differences between chromosomes and circular DNA. For instance, high-speed ultracentrifugation in cesium-chloride gradients is used to isolate 350-3000 basepairs (bp) large eccDNAs from the human HeLa cancer cell line14. However, high-velocity can break or nick the backbone of supercoiled circular DNA structures, altering the sedimentation velocity15 and the eccDNA yield. Dutta and coworkers developed a method for de novo, genome-scale identification of circular DNA from mouse tissues as well as from cultures of chicken and human cells16,17. Their method is extraction of nuclei from homogenized tissue by sucrose ultracentrifugation followed by plasmid purification and several rounds of enzymatic reactions and DNA extractions. Their protocol primarily identifies 200-400 bp eccDNAs, called microDNAs. Dutta and coworkers also attempted purification of microDNAs from Saccharomyces cerevisiae but were unable to record microDNA from this yeast species16.
We have developed a novel method for de novo detection of eccDNA from yeast called Circle-Seq. This method enables genome-scale surveys for circular DNA molecules large enough to carry whole genes and as large as the 86 kilobase (kb) mitochondrial DNA (mtDNA). The Circle-Seq method was developed from a well-established prokaryotic plasmid purification method18,19, optimized for eukaryotic yeast cells and combined with deep&#160;sequencing. Using the Circle-Seq approach, 1756 different eccDNAs, all larger than 1 kb, were detected from ten S. cerevisiae S288c populations20. A size cut-off was chosen to focus on eccDNA that were&#160;large enough to carry whole genes. Circle-Seq was highly sensitive; it detected a single eccDNA within thousands of cells20. In the current study, Circle-Seq was used to isolate and identify 294 eccDNAs from three biological replicates of another S. cerevisiae yeast strain, CEN.PK. The data reveals that eccDNA is a common genetic element in S. cerevisiae strains.

<table><tbody><tr><td>Bacto peptone</td><td>BD Difco</td><td>211677</td><td>Alternative product can be used.</td></tr><tr><td>Brilliant III SYBR Green PCR Master Mix&amp;nbsp;</td><td>Agilent Technologies</td><td>600882</td><td>For qPCR analysis. Alternative product can be used.</td></tr><tr><td>Dextrose (D-glucose)</td><td>Carl Roth</td><td>HN06.4</td><td>Alternative product can be used.</td></tr><tr><td>Disruptor Beads, 0.5 mm</td><td>Scientific Industries, Inc.</td><td>SI-BG05</td><td>Glass beads to disrupt plasma cell membranes. Alternative product can be used.</td></tr><tr><td>Ethidium bromide</td><td>Carl Roth</td><td>2218.2</td><td>Agarose gel stain for detecting DNA/RNA.</td></tr><tr><td>GeneJet plasmid miniprep kit</td><td>Thermo Fisher</td><td>K0502</td><td>Plasmid purifcation from bacteria. Alternative product can be used.</td></tr><tr><td>NotI, FastDigest</td><td>Life Technologies -&amp;nbsp; Thermo Fisher Scientific, USA</td><td>FD0594</td><td>Endonuclease. Alternative product can be used.&amp;nbsp;</td></tr><tr><td>Plasmid Mini AX kit&amp;nbsp;</td><td>A&amp;amp;A Biotechnology, Poland</td><td>010-50</td><td>Plasmid purifcation kit used to purify eccDNA.&amp;nbsp;&amp;nbsp;</td></tr><tr><td>Plasmid-Safe ATP-dependent DNase kit</td><td>Epicentre, USA</td><td>E3105K</td><td>ATP-dependent exonuclease kit. Alternative product can be used.</td></tr><tr><td>Propidium iodide&amp;nbsp;</td><td>Sigma-Aldrich, USA</td><td>81845</td><td>Alternative product can be used.</td></tr><tr><td>pUG6 plasmid</td><td>EUROSCARF, Germany</td><td>P30114</td><td>Marker gene: loxP-PAgTEF1-kanMX-TAgTEF1-loxP.</td></tr><tr><td>QIAGEN genomic-tip 100/G&amp;nbsp;</td><td>Qiagen, USA</td><td>13343</td><td>Genomic DNA purifcation from yeast. Alternative product can be used.</td></tr><tr><td>REPLI-g Mini Kit protocol&amp;nbsp;</td><td>Qiagen, USA</td><td>150023</td><td>Amplification of eccDNA by the phi29 polymerase.</td></tr><tr><td>Yeast extract</td><td>BD Difco</td><td>210929</td><td>Alternative product can be used.</td></tr><tr><td>Zymolyase 100T (Lyticase, Yeast Lytic Enzyme)</td><td>Nordic BioSite, Sweden</td><td>Z1004-3</td><td>Alternative product can be used.</td></tr><tr><td>&lt;strong&gt;Data access to sequence files&lt;/strong&gt;</td><td>European Nucleotide Archive&amp;nbsp;</td><td></td><td>EccDNA dataset from &lt;i&gt;Saccharomyces cerevisiae&lt;/i&gt; CEN.PK113-7D. Study accession number PRJEB9684. 2nd accession number is ERP010820. Locus tag prefix is BN2032.&amp;nbsp;</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Strains&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>&lt;i&gt;Saccharomyces cerevisiae&lt;/i&gt; CEN.PK113-7D</td><td></td><td></td><td>Genotype MATa MAL2-8c SUC2</td></tr><tr><td>&lt;i&gt;Saccharomyces cerevisiae&lt;/i&gt; yeast deletion library pool</td><td>EUROSCARF, Germany</td><td></td><td>S288c BY4741 pool of 4400 viable single-gene deletion mutants disrubted by KanMX module. Genotypes &lt;em&gt;MAT&lt;strong&gt;a&lt;/strong&gt; his3&amp;Delta;1 leu2&amp;Delta;0 met15&amp;Delta;0 ura3&amp;Delta;0 genexxx::KanMX.&lt;/em&gt;</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipments&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>DNA Spectrophotometer&amp;nbsp;</td><td>NanoDrop 1000 Spectrophotometer, Thermo Fisher</td><td></td><td>Measuring DNA concentration. Alternative product can be used.</td></tr><tr><td>Fluorescence microscopy</td><td>Nikon Optronics Magnafire. Red excitation fluorescence filter, 663-738 nm.</td><td></td><td>Alternative product can be used.</td></tr><tr><td>Robotic library-build system</td><td>Apollo 324, IntegenX Inc.</td><td></td><td>DNA library preparation. Alternative product can be used.</td></tr><tr><td>Sequencing platform</td><td>Illumina HiSeq 2000 platform, Illumina Inc.</td><td></td><td>DNA sequencing. Alternative product can be used.</td></tr><tr><td>Ultrasonicator</td><td>Covaris LE220, microTUBE AFA Fiber tubes</td><td></td><td>Alternative product can be used.</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Methods&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>2% YPD media&amp;nbsp;</td><td></td><td></td><td>Mix 10 g Dextrose, 10 g Yeast extract, 20 g Bacto peptone and add H2O to a total volume of 1000 ml and autoclave.</td></tr><tr><td>Circle-Seq test on genomic DNA</td><td></td><td></td><td>Genomic DNA was purified (Qiagen) from a pool of the yeast deletion library (Euroscarf). The DNA concentration was measured by nanodrop and 30 &amp;micro;g genomic DNA was pipetted into two micro centrifuge tubes. One micro centrifuge tube was supplemented with 100 nanogram plasmid (pUG6). The DNA samples were purified by Circle-Seq, omitting the protocol steps 1.1-1.3 and 1.5-1.7. The eluted DNA concentrations were measured by nanodrop and the entire DNA yield from sample GD and GD+P was treated with exonuclease for a period of 29 hours. A 10% fraction was collected for phi29-amplification and PCR analysis, while the remaining DNA was subjected to 72 hour exonuclease treatment. The samples were analyzed for linear DNA content by PCR, using the &lt;i&gt;ACT1&lt;/i&gt; gene as chromosomal marker. A 5% fraction of each of the exonuclease treated samples was amplified by the phi29 DNA polymerase for 16 hours (Qiagen). The presence of DNA in each sample was examined by loading an equal amount (7 &amp;micro;l) in wells on an 0.5 &amp;micro;g/ml ethidium-bromide 0.9% agarose gel after running gel-electrophoresis.&amp;nbsp;</td></tr><tr><td>Mapping software</td><td>Bowtie2 aligner, John Hopkins University</td><td></td><td>Ultrafast short read alignment. Reference: 29.</td></tr><tr><td>Propidium iodide stain</td><td></td><td></td><td>Images of propidium iodine stained DNA were captured by fluorescence microscopy at 100x magnification (100x/1.30 oil, Nikon) in the RFP channel (red excitation fluorescence filter, 663-738 nm) using identical exposition time (5 seconds).&amp;nbsp;</td></tr><tr><td>Workflow bioinformatic system</td><td>Galaxy, Open source.</td><td></td><td>A free web-based platform for data intensive biomedical research. References: 27-28.</td></tr></tbody></table>

genome-wide purification of extrachromosomal circular dna from eukaryotic cells

Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs contribute to genetic variation among somatic cells in multicellular organisms and to evolution of unicellular eukaryotes. Sensitive methods for detecting eccDNA are needed to clarify how these elements affect genome stability and how environmental and biological factors&#160;induce their formation in eukaryotic cells. This video presents a sensitive eccDNA-purification method called Circle-Seq. The method encompasses column purification of circular DNA, removal of remaining linear chromosomal DNA, rolling-circle amplification of eccDNA, deep sequencing, and mapping. Extensive exonuclease treatment&#160;was&#160;required for sufficient linear chromosomal DNA degradation. The rolling-circle amplification step by &#966;29 polymerase enriched for circular DNA over linear DNA. Validation of the Circle-Seq method on three S. cerevisiae CEN.PK populations of 1010 cells detected hundreds of eccDNA profiles in sizes larger than 1 kilobase. Repeated findings of ASP3-1, COS111, CUP1, RSC30,&#160;HXT6, HXT7 genes on circular DNA in both S288c and CEN.PK suggests that DNA circularization is conserved between strains at these loci. In sum, the Circle-Seq method has broad applicability for genome-scale screening for eccDNA in eukaryotes as well as for detecting specific eccDNA types.

To validate the Circle-Seq method, three S. cerevisiae CEN.PK populations of 1 x 1010 cells were screened after cells were grown separately in YPD for ten generations. Chromosomal linear DNA elimination was confirmed by the absence of a qPCR ACT1 signal as described previously20 (data not shown). Purified and enriched eccDNA was sequenced up to 68 million reads (141-nucleotide single-end reads) and mapped to the CEN.PK113-7D reference genome (version 19 June 2012). Recordings of putative eccDNAs from the three samples named C1, C2 and C4 were assigned to genomic regions mapped by contiguous reads longer than 1 kb. Based on 10,000 Monte Carlo simulations, the significance of each region mapped by contiguous reads longer than 1 kb was estimated. From this 79, 159 and 56 regions were annotated as likely eccDNA sequences (p &#60; 0.1, Dataset 1). The number of recorded contiguous reads &#62; 1 kb increased as a function of sequence depth suggesting that even more eccDNA elements would have been recorded if samples had been sequenced further (Figure&#160;2). As expected, the Circle-Seq method extracted numerous reads from a number of known circular DNA elements including the 2&#181; plasmid, mitochondrial DNA, ribosomal RNA genes on chromosome XII, and the three internal control plasmids pBR322, pUC19 and pUG72 that were spiked into samples just before column purification (Figure 3).
The video shows an example of contiguous reads that mapped to the HXT7_ARS432_HXT6 locus on chromosome IV. Previously, the [HXT6/7circle] was detected by Circle-Seq in ten S288c populations (each with 1 x 1010 cells) and the circular DNA structure was confirmed by inverse PCR analysis20. The [HXT6/7circle] was also recorded in each of the three CEN.PK populations (Figure 4A). Moreover, most of the common eccDNA genes among replicate samples of CEN.PK overlapped eccDNA genes from the S288c datasets (Figure 4B).
To test the specificity of the Circle-Seq protocol for circular DNA purification, two samples, each with 30 &#181;g genomic DNA, were tested. One sample was supplemented with 100 ng plasmid DNA and eccDNA from both&#160;samples were purified by the Circle-Seq protocol. After column separation, the DNA yield was 1.27% (380 ng) for the sample without plasmid (GD) and 1.60% (480 ng) for the sample with plasmid (GD+P). The efficiency of exonuclease treatment was tested for linear DNA content after 29 hr&#160;and 72 hr&#160;using PCR against ACT1. No samples contained amplified ACT1 (data not shown). A fraction of each exonuclease-treated sample was further amplified by the &#248;29 polymerase and the products of enzymatic reactions were analyzed by propidium iodide staining (Figure 5A-F) and agarose gel electrophoresis (Figure 5G). Samples after exonuclease treatment showed minimal propidium iodine-stain (Figure 5A-B). The &#248;29-amplified sample with only genomic DNA revealed thread-like structures (Figure 5C) similar to the control sample (Figure 5E). The &#248;29-amplified sample that had added plasmid revealed foci (Figure 5D)&#160;resembling the plasmid control (Figure 5F). The images indicated that &#248;29 polymerase enriched for circular DNA over linear DNA. Most linear chromosomal DNA was removed from samples after 29 hr exonuclease treatment (Figure 5A-B, G). However, extensive exonuclease treatment for more than 100 hr and using more than 100 units&#160;was needed to remove all chromosomal linear DNA, as &#248;29-amplified&#160;samples still showed a background of thread-like structures after 72 hr exonuclease treatment (Figure 5C-D).
<img alt="Figure 1" src="/files/ftp_upload/54239/54239fig1.jpg" /> 
Figure 1. Outline of the Circle-Seq method. The protocol has 5 steps: 1) cell culturing, 2) purification and enrichment of eccDNA by column chromatography, 3) digestion of remaining linear chromosomal DNA in the eluate fraction, 4) amplification of DNA by &#248;29 DNA polymerase, and 5) sequencing of highly enriched eccDNA and mapping of reads to the S. cerevisiae reference genome. <a href="https://www.jove.com/files/ftp_upload/54239/54239fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/54239/54239fig2.jpg" /> 
Figure 2. Contiguous reads &#62; 1 kb as function of sequence depth. EccDNA from 1 x 1010 cells increase as a function of sequence depth (in millions of mapped reads). Shown: biological triplicates from haploid CEN.PK S. cerevisiae populations (C1, C2, C4) separated by 1010 cell divisions. <a href="https://www.jove.com/files/ftp_upload/54239/54239fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/54239/54239fig3.jpg" /> 
Figure 3. Detection of known circular DNA elements.&#160;(A-B) Scatter plots of read coverage (read density) in percent for plasmids in CEN.PK biological replicates C1, C2 and C4. (A) Mapped reads to the endogenous yeast plasmids were: 2&#181;; [rDNAcircle] (ribosomal RNA genes from chromosome XII); and mtDNA (the mitochondrial DNA). (B) Unique reads mapped to control plasmids. Control plasmids were spiked into samples before column purification. Plasmid ratios per cell were: pBR322 (plus signs) 1:1, pUC19 (circles) 1:50, and pUG72 (triangles) 1:2,500.
<img alt="Figure 4" src="/files/ftp_upload/54239/54239fig4.jpg" /> 
Figure 4. Common eccDNA elements in CEN.PK and S288c. (A) Venn diagram displaying overlap among the 476 genes on 294 eccDNA elements in the three CEN.PK samples (C1, C2, C4). The 16 common overlapping eccDNA genes/plasmids are annotated (all gene names are in Dataset 1). (B) Venn diagram of all recorded genes on putative eccDNAs from the three CEN.PK samples (C1, C2, C4), compared to all recorded genes on putative eccDNAs from 10 S288c samples: S1-S2, R1-R4, Z1-Z4 (see reference20). Shown are 13 biological replicates (S1-S2, R1-R4, Z1-Z4, C1-C3) with genes/plasmids and putative eccDNA regions that overlapped a minimum of 2 strain backgrounds and either 3 or more experimental setups. C samples, CEN.PK; R and Z samples, S288c BY4741; S samples, S288c M3750. <a href="https://www.jove.com/files/ftp_upload/54239/54239fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/54239/54239fig5.jpg" /> 
Figure 5. Visualization of DNA samples after exonuclease and &#248;29 treatment. (A-F) Propidium iodide staining of DNA. Scale bar, 10 &#181;m. (A, C and E) Samples with genomic DNA (GD); (B and D)&#160;samples with GD plus plasmid (GD+P). (A-B) After 29 hr exonuclease treatment (EXO 29 h); (C-D) after 72 hr exonuclease treatment followed by &#248;29 polymerase amplification (EXO 72 h + &#248;29). (E) Genomic DNA control after e: &#248;29 polymerase amplification; (F) plasmid control (5.5 kb) after 29 polymerase amplification; (G&#248;) agarose gel-eletrophoresis. From left: L, 1 kb&#160;markers; P, plasmid control (5.5 kb) after EXO 29 hr; GD, after EXO 29 hr (sample as in A); GD+P, after EXO 29 hr (sample as B); GD and GD+P, after EXO 29 hr + &#248;29; GD and GD+P, after EXO 72 hr + &#248;29 (sample as in C-D). See Table S1 for extra details. <a href="https://www.jove.com/files/ftp_upload/54239/54239fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Dataset 1" src="/files/ftp_upload/54239/54239dataset1.jpg" /> 
Dataset 1. Potential DNA circularization regions in CEN.PK. <a href="https://www.jove.com/files/ftp_upload/54239/DATASET1-CENPK.xlsx">Please click here to download this file.</a> 
Shown are sequence data and analyses for 348 regions. Columns are A-D, eccDNA mapping. A (first column from left), sample from which putative eccDNA was identified; B, chromosome; C-D, start and end coordinates of putative eccDNAs. E-H, eccDNA content. E, autonomously replicating sequence (ARS) in the region; F, complete gene in the region; G, part of gene included in the region; H, BLASTN-identified gene. I-O, EccDNA coverage and p-values. I, longest region with a uniquely annotated sequence in bp; J, number of all mapped reads; K, coverage of all mapped reads by fragments per kb from a million mapped reads (FPKM); L, p-value for putative eccDNA compared to occurrence by chance from Monte Carlo simulations; M, number of uniquely mapped reads; N-O; as K and L using only uniquely mapped reads (UFPKM). Parameters for mapping of reads and Monte Carlo simulations were as described20.

Watch this Scientific Journal Video about Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells at JoVE.com

Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells

This paper presents a sensitive method called Circle-Seq for purifying extrachromosomal circular DNA (eccDNA). The method encompasses column purification, removal of remaining linear chromosomal DNA, rolling-circle amplification and high-throughput sequencing. Circle-Seq is applicable to genome-scale screening of eukaryotic eccDNA and studying genome instability and copy-number variation.

Extrachromosomal circular DNAs (eccDNAs) are common genetic elements in Saccharomyces cerevisiae and are reported in other eukaryotes as well. EccDNAs ...

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Biology

25.1K Views.  University of Copenhagen. This paper presents a sensitive method called Circle-Seq for purifying extrachromosomal circular DNA (eccDNA). The method encompasses column purification, removal of remaining linear chromosomal DNA, rolling-circle amplification and high-throughput sequencing. Circle-Seq is applicable to genome-scale screening of eukaryotic eccDNA and studying genome instability and copy-number variation. 

Video: Genome-wide Purification of Extrachromosomal Circular DNA from Eukaryotic Cells

Purification of High Molecular Weight Genomic DNA from Powdery Mildew for Long-Read Sequencing

The powdery mildew fungi are a group of economically important fungal plant pathogens. Relatively little is known about the molecular biology and genetics of these pathogens, in part due to a lack of well-developed genetic and genomic resources. These organisms have large, repetitive genomes, which have made genome sequencing and assembly prohibitively difficult. Here, we describe methods for the collection, extraction, purification and quality control assessment of high molecular weight genomic DNA from one powdery mildew species, Golovinomyces cichoracearum. The protocol described includes mechanical disruption of spores followed by an optimized phenol/chloroform genomic DNA extraction. A typical yield was 7 &#181;g DNA per 150 mg conidia. The genomic DNA that is isolated using this procedure is suitable for long-read sequencing (i.e., &#62; 48.5 kbp). Quality control measures to ensure the size, yield, and purity of the genomic DNA are also described in this method. Sequencing of the genomic DNA of the quality described here will allow for the assembly and comparison of multiple powdery mildew genomes, which in turn will lead to a better understanding and improved control of this agricultural pathogen.

Described here is a method for the extraction, purification, and quality control of genomic DNA from the obligate biotrophic fungal pathogen, powdery mildew, for use in long-read genome sequencing.

The powdery mildew fungi are a group of economically important fungal plant pathogens. Relatively little is known about the molecular biology and genetics ...

Genetics

Purifying Plasmid DNA from Bacterial Colonies Using the Qiagen Miniprep Kit

Plasmid DNA purification from E. coli is a core technique for molecular cloning. Small scale purification (miniprep) from less than 5 ml of bacterial culture is a quick way for clone verification or DNA isolation, followed by further enzymatic reactions (polymerase chain reaction and restriction enzyme digestion). Here, we video-recorded the general procedures of miniprep through the QIAGEN's QIAprep 8 Miniprep Kit, aiming to introducing this highly efficient technique to the general beginners for molecular biology techniques. The whole procedure is based on alkaline lysis of E. coli cells followed by adsorption of DNA onto silica in the presence of high salt. It consists of three steps: 1) preparation and clearing of a bacterial lysate, 2) adsorption of DNA onto the QIAprep membrane, 3) washing and elution of plasmid DNA. All steps are performed without the use of phenol, chloroform, CsCl, ethidium bromide, and without alcohol precipitation. It usually takes less than 2 hours to finish the entire procedure.

Plasmid DNA purification from E. coli is a core technique for molecular cloning. Small scale purification (miniprep) from less than 5 ml of bacterial ...

Novel Sequence Discovery by Subtractive Genomics

Subtractive genomics can be used in any research where the goal is to identify the sequence of a gene, protein, or general region that is embedded in a larger genomic context. Subtractive genomics enables a researcher to isolate a target sequence of interest (T) by comprehensive sequencing and subtracting out known genetic elements (reference, R). The method can be used to identify novel sequences such as mitochondria, chloroplasts, viruses, or germline restricted chromosomes, and is particularly useful when T cannot be easily isolated from R. Beginning with the comprehensive genomic data (R + T), the method uses Basic Local Alignment Search Tool (BLAST) against a reference sequence, or sequences, to remove the matching known sequences (R), leaving behind the target (T). For subtraction to work best, R should be a relatively complete draft that is missing T. Since sequences remaining after subtraction are tested through quantitative Polymerase Chain Reaction (qPCR), R does not need to be complete for the method to work. Here we link computational steps with experimental steps into a cycle that can be iterated as needed, sequentially removing multiple reference sequences and refining the search for T. The advantage of subtractive genomics is that a completely novel target sequence can be identified even in cases in which physical purification is difficult, impossible, or expensive. A drawback of the method is finding a suitable reference for subtraction and obtaining T-positive and negative samples for qPCR testing. We describe our implementation of the method in the identification of the first gene from the germline-restricted chromosome of zebra finch. In that case computational filtering involved three references (R), sequentially removed over three cycles: an incomplete genomic assembly, raw genomic data, and transcriptomic data.

The purpose of this protocol is to use a combination of computational and bench research to find novel sequences that cannot be easily separated from a co-purifying sequence, which may be only partially known.

Subtractive genomics can be used in any research where the goal is to identify the sequence of a gene, protein, or general region that is embedded in a ...

A Comprehensive Approach to Studying the Promoter Interactome in Scarce Cells

An Integrated Workflow to Study the Promoter-Centric Spatio-Temporal Genome Architecture in Scarce Cell Populations

Spatiotemporal gene transcription is tightly regulated by distal regulatory elements, such as enhancers and silencers, which rely on physical proximity with their target gene promoters to control transcription. Although these regulatory elements are easy to identify, their target genes are difficult to predict, since most of them are cell-type specific and may be separated by hundreds of kilobases in the linear genome sequence, skipping over other non-target genes. For several years, Promoter Capture Hi-C (PCHi-C) has been the gold standard for the association of distal regulatory elements to their target genes. However, PCHi-C relies on the availability of millions of cells, prohibiting the study of rare cell populations such as those commonly obtained from primary tissues. To overcome this limitation, low input Capture Hi-C (liCHi-C), a cost-effective and customizable method to identify the repertoire of distal regulatory elements controlling each gene of the genome, has been developed. liCHi-C relies on a similar experimental and computational framework as PCHi-C, but by employing minimal tube changes, modifying&#160;the reagent concentration and volumes, and swapping or eliminating steps, it accounts&#160;for minimal material loss during library construction. Collectively, liCHi-C enables the study of gene regulation and spatiotemporal genome organization in the context of developmental biology and cellular function.

Author Spotlight: An Integrated Workflow to Study the Promoter-Centric Spatio-Temporal Genome Architecture in Scarce Cell Populations  

Gene expression is regulated by interactions of gene promoters with distal regulatory elements. Here, we descirbe how low input Capture Hi-C (liCHi-C) allows the identification of these interactions in rare cell types, which were previously unmeasurable.

Spatiotemporal gene transcription is tightly regulated by distal regulatory elements, such as enhancers and silencers, which rely on physical proximity ...

Detecting Off-Target CRISPR-Cas9 Cleavage Events with CIRCLE-Seq

CIRCLE-Seq for Interrogation of Off-Target Gene Editing

Circularization for In Vitro Reporting of Cleavage Effects by Sequencing (CIRCLE-seq) is a novel technique developed for the impartial identification of unintended cleavage sites of CRISPR-Cas9 through targeted sequencing of CRISPR-Cas9 cleaved DNA. The protocol involves circularizing genomic DNA (gDNA), which is subsequently treated with the Cas9 protein and a guide RNA (gRNA) of interest. Following treatment, the cleaved DNA is purified and prepared as a library for Illumina sequencing. The sequencing process generates paired-end reads, offering comprehensive data on each cleavage site. CIRCLE-seq provides several advantages over other in vitro methods, including minimal sequencing depth requirements, low background, and high enrichment for Cas9-cleaved gDNA. These advantages enhance sensitivity in identifying both intended and unintended cleavage events. This study provides a comprehensive, step-by-step procedure for examining the off-target activity of CRISPR-Cas9 using CIRCLE-seq. As an example, this protocol is validated by mapping genome-wide unintended cleavage sites of CRISPR-Cas9 during the modification of the AAVS1 locus. The entire CIRCLE-seq process can be completed in two weeks, allowing sufficient time for cell growth, DNA purification, library preparation, and Illumina sequencing. The input of sequencing data into the CIRCLE-seq pipeline facilitates streamlined interpretation and analysis of cleavage sites.

A significant barrier to technologies like CRISPR is the off-target events that can disrupt vital genes. 'Circularization for In Vitro Reporting of Cleavage Effects by Sequencing' (CIRCLE-seq) is a technique designed to identify unintended cleavage sites. This method maps the genome-wide activity of CRISPR-Cas9 with high sensitivity and without bias.

Circularization for In Vitro Reporting of Cleavage Effects by Sequencing (CIRCLE-seq) is a novel technique developed for the impartial identification of ...

Extraction of High Molecular Weight Genomic DNA from Soils and Sediments

The soil microbiome is a vast and relatively unexplored reservoir of genomic diversity and metabolic innovation that is intimately associated with nutrient and energy flow within terrestrial ecosystems. Cultivation-independent environmental genomic, also known as metagenomic, approaches promise unprecedented access to this genetic information with respect to pathway reconstruction and functional screening for high value therapeutic and biomass conversion processes. However, the soil microbiome still remains a challenge largely due to the difficulty in obtaining high molecular weight DNA of sufficient quality for large insert library production. Here we introduce a protocol for extracting high molecular weight, microbial community genomic DNA from soils and sediments. The quality of isolated genomic DNA is ideal for constructing large insert environmental genomic libraries for downstream sequencing and screening applications. 
The procedure starts with cell lysis. Cell walls and membranes of microbes are lysed by both mechanical (grinding) and chemical forces (&beta;-mercaptoethanol). Genomic DNA is then isolated using extraction buffer, chloroform-isoamyl alcohol and isopropyl alcohol. The buffers employed for the lysis and extraction steps include guanidine isothiocyanate and hexadecyltrimethylammonium bromide (CTAB) to preserve the integrity of the high molecular weight genomic DNA. Depending on your downstream application, the isolated genomic DNA can be further purified using cesium chloride (CsCl) gradient ultracentrifugation, which reduces impurities including humic acids. The first procedure, extraction, takes approximately 8 hours, excluding DNA quantification step. The CsCl gradient ultracentrifugation, is a two days process. During the entire procedure, genomic DNA should be treated gently to prevent shearing, avoid severe vortexing, and repetitive harsh pipetting.

A methodology to isolate high molecular weight and high quality genomic DNA from soil microbial community is described.

The soil microbiome is a vast and relatively unexplored reservoir of genomic diversity and metabolic innovation that is intimately associated with ...

Streamlined Purification of Plasmid DNA From Prokaryotic Cultures

We describe the complete process of AcroPrep Advance Filter Plates for 96 plasmid preparations, starting from prokaryotic culture and ending with high purity DNA. Based on multi-well filtration for bacterial lysate clearance and DNA purification, this method creates a streamlined process for plasmid preparation. Filter plates containing silica-based media can easily be processed by vacuum filtration or centrifuge to yield appreciable quantities of plasmid DNA. Quantitative analyses determine the purified plasmid DNA is consistently of high quality with average OD260/280 ratios of 1.97. Overall, plasmid yields offer more pure DNA for downstream applications, such as sequencing and cloning. This streamlined method of using AcroPrep Advance Filter Plates allows for manual, semi-automated or fully-automated processing.

This protocol is a cost effective alternative for efficient parallel clarification and plasmid DNA purification from E. coli cultures. The AcroPrep Advance process starts with an optimized lysate clarification filter plate followed by purification on a high binding capacity DNA binding filter plate.

We describe the complete process of AcroPrep Advance Filter Plates for 96 plasmid preparations, starting from prokaryotic culture and ending with high ...

Locus-Specific Chromatin Isolation from Yeast Cells

Single-Copy Gene Locus Chromatin Purification in Saccharomyces cerevisiae

The basic organizational unit of eukaryotic chromatin is the nucleosome core particle (NCP), which comprises DNA wrapped ~1.7 times around a histone octamer. Chromatin is defined as the entity of NCPs and numerous other protein complexes, including transcription factors, chromatin remodeling and modifying enzymes. It is still unclear how these protein-DNA interactions are orchestrated at the level of specific genomic loci during different stages of the cell cycle. This is mainly due to the current technical limitations, which make it challenging to obtain precise measurements of such dynamic interactions. Here, we describe an improved method combining site-specific recombination with an efficient single-step affinity purification protocol to isolate a single-copy gene locus of interest in its native chromatin state. The method allows for the robust enrichment of the target locus over genomic chromatin, making this technique an effective strategy for identifying and quantifying protein interactions in an unbiased and systematic manner, for example by mass spectrometry. Further to such compositional analyses, native chromatin purified by this method likely reflects the in vivo situation regarding nucleosome positioning and histone modifications and is, therefore, amenable to further structural and biochemical analyses of chromatin derived from virtually any genomic locus in yeast.

Author Spotlight: Advancing Chromatin Research and Overcoming Limitations with a High-Enrichment Locus-Specific Chromatin Isolation Protocol 

This protocol presents a locus-specific chromatin isolation method based on site-specific recombination to purify a single-copy gene locus of interest in its native chromatin context from budding yeast, Saccharomyces cerevisiae.

The basic organizational unit of eukaryotic chromatin is the nucleosome core particle (NCP), which comprises DNA wrapped ~1.7 times around a histone ...

Biochemistry

Generation and Purification of Human INO80 Chromatin Remodeling Complexes and Subcomplexes

INO80 chromatin remodeling complexes regulate nucleosome dynamics and DNA accessibility by catalyzing ATP-dependent nucleosome remodeling. Human INO80 complexes consist of 14 protein subunits including Ino80, a SNF2-like ATPase, which serves both as the catalytic subunit and the scaffold for assembly of the complexes. Functions of the other subunits and the mechanisms by which they contribute to the INO80 complex&#39;s chromatin remodeling activity remain poorly understood, in part due to the challenge of generating INO80 subassemblies in human cells or heterologous expression systems. This JOVE protocol describes a procedure that allows purification of human INO80 chromatin remodeling subcomplexes that are lacking a subunit or a subset of subunits. N-terminally FLAG epitope tagged Ino80 cDNA are stably introduced into human embryonic kidney (HEK) 293 cell lines using Flp-mediated recombination. In the event that a subset of subunits of the INO80 complex is to be deleted, one expresses instead mutant Ino80 proteins that lack the platform needed for assembly of those subunits. In the event an individual subunit is to be depleted, one transfects siRNAs targeting this subunit into an HEK 293 cell line stably expressing FLAG tagged Ino80 ATPase. Nuclear extracts are prepared, and FLAG immunoprecipitation is performed to enrich protein fractions containing Ino80 derivatives. The compositions of purified INO80 subcomplexes can then be analyzed using methods such as immunoblotting, silver staining, and mass spectrometry. The INO80 and INO80 subcomplexes generated according to this protocol can be further analyzed using various biochemical assays, which are described in the accompanying JOVE protocol. The methods described here can be adapted for studies of the structural and functional properties of any mammalian multi-subunit chromatin remodeling and modifying complexes.

This protocol describes a procedure for generating and purifying wild type and mutant versions of the human INO80 chromatin remodeling complex. Epitope tagged versions of INO80 subunits are stably expressed in HEK293 cells, and complete complexes and complexes lacking specific sets of subunits are purified by immunoaffinity chromatography.

INO80 chromatin remodeling complexes regulate nucleosome dynamics and DNA accessibility by catalyzing ATP-dependent nucleosome remodeling. Human INO80 ...

Efficient Technique for Assessing Environmental AMR by Enriching Low-MW DNA

Enhanced Extraction of Low-Molecular Weight DNA from Wastewater for Comprehensive Assessment of Antimicrobial Resistance

Environmental surveillance is recognized as an important tool for assessing public health in the post-pandemic era. Water, in particular wastewater, has emerged as the source of choice to sample pathogen burdens in the environment. Wastewater from open drains and community water treatment plants is a reservoir of both pathogens and antimicrobial resistance (AMR) genes, and frequently comes in contact with humans. While there are many methods of tracking AMR from water,&#160;isolating good-quality DNA at high yields from heterogeneous samples remains a challenge. To compensate, sample volumes often need to be high, creating practical constraints. Additionally, environmental DNA is frequently fragmented, and the sources of AMR (plasmids, phages, linear DNA) consist of low-molecular-weight DNA. Yet, few extraction processes have focused on methods for high-yield extraction of linear and low-molecular-weight DNA. Here, a simple method for high-yield linear DNA extraction from small volumes of wastewater using the precipitation properties of polyethylene glycol (PEG) is reported. This study makes a case for increasing overall DNA yields from water samples collected for metagenomic analyses by enriching the proportion of linear DNA. In addition, enhancing low-molecular-weight DNA overcomes the current problem of under-sampling environmental AMR due to a focus on high-molecular-weight and intracellular DNA. This method is expected to be particularly useful when extracellular DNA exists but at low concentrations, such as with effluents from treatment plants. It should also enhance the environmental sampling of AMR gene fragments that spread through horizontal gene transfer.

Author Spotlight: Understanding and Detecting Environmental Antimicrobial Resistance by Combining Culture-Based Techniques and Genomics

Here, we present a simple technique to assess environmental antimicrobial resistance (AMR) by enhancing the proportion of low-molecular-weight extracellular DNA. Prior treatment with 20%-30% PEG and 1.2 M NaCl allows detection of both genomic and horizontally transferred AMR genes. The protocol lends itself to a kit-free process with additional optimization.

Environmental surveillance is recognized as an important tool for assessing public health in the post-pandemic era. Water, in particular wastewater, has ...