Name: inducing a site specific replication blockage in e. coli using a fluorescent repressor operator system
Uploaded: 2016-08-21T15:00:00
Description: Watch this Scientific Journal Video about Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System at JoVE.com

This work was supported by the Australian Research Council [DP11010246].

1. Blocking Replication with FROS
<ol>
	<li>Inducing the Replication Blockage
	<ol>
		<li>Dilute a fresh overnight culture of an E. coli strain carrying a tetO array and pKM118 to OD600nm = 0.01 in a dilute complex medium (0.1% tryptone, 0.05% yeast extract, 0.1% NaCl, 0.17 M KH2PO4, 0.72 M K2HPO4) with antibiotics as required for selection. 
		Note: Do not add tetracycline for selection as it is not compatible with this system. Ma...

<ol>
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T., 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=Replication+fork+blockage+by+transcription+factor-DNA+complexes+in+Escherichia+coli.">Replication fork blockage by transcription factor-DNA complexes in Escherichia coli.</a> Nucleic Acids Res. 34 (18), 5194-5202 (2006).</li><li>Brewer, B. J., Fangman, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+localization+of+replication+origins+on+ARS+plasmids+in+S.+cerevisiae.">The localization of replication origins on ARS plasmids in S. cerevisiae.</a> Cell. 51 (3), 463-471 (1987).</li><li>Jeiranian, H. A., Schalow, B. J., Courcelle, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+UV-induced+replication+intermediates+in+E.+coli+using+two-dimensional+agarose-gel+analysis.">Visualization of UV-induced replication intermediates in E. coli using two-dimensional agarose-gel analysis.</a> J Vis Exp. (46), (2010).</li><li>Southern, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+specific+sequences+among+DNA+fragments+separated+by+gel+electrophoresis.">Detection of specific sequences among DNA fragments separated by gel electrophoresis.</a> J Mol Biol. 98 (3), 503-517 (1975).</li><li>Courcelle, J., Donaldson, J. R., Chow, K. H., Courcelle, C. 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J., Bidnenko, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+pathways+process+stalled+replication+forks.">Multiple pathways process stalled replication forks.</a> Proc Natl Acad Sci U S A. 101 (35), 12783-12788 (2004).</li><li>Michel, B., Boubakri, H., Baharoglu, Z., LeMasson, M., Lestini, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recombination+proteins+and+rescue+of+arrested+replication+forks.">Recombination proteins and rescue of arrested replication forks.</a> DNA Repair (Amst). 6 (7), 967-980 (2007).</li><li>Carl, P. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Escherichia+coli+mutants+with+temperature-sensitive+synthesis+of+DNA.">Escherichia coli mutants with temperature-sensitive synthesis of DNA.</a> Mol Gen Genet. 109 (2), 107-122 (1970).</li><li>Nawotka, K. A., Huberman, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+gel+electrophoretic+method+for+mapping+DNA+replicons.">Two-dimensional gel electrophoretic method for mapping DNA replicons.</a> Mol Cell Biol. 8 (4), 1408-1413 (1988).</li><li>Cole, R. S., Levitan, D., Sinden, R. 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During chromosome duplication, the replication machinery will encounter various impediments that prevent its progress. To ensure the entire single-origin chromosome is replicated, bacteria have numerous pathways for repair of the DNA that then enables the replisome to be reloaded20,21. Lesions, single stranded breaks, double stranded breaks and proteins tightly bound to the DNA may each be dealt with using a dedicated pathway, although there is likely to be significant overlap in these pathways. The most commo...

During DNA replication, the replisome faces obstacles on the DNA that impair its progression. DNA damage including lesions and gaps as well as aberrant structures can prevent the replisome from proceeding1. Recently, it has been found that proteins bound to the DNA are the most common source of impediment to replication fork progression2. The knowledge of the events following the encounter of the replisome with a nucleoprotein block has previously been limited by the inability to induce such a block in the chromosome of a living cell at a known location. In vitro analysis has enhanced our understanding of the kinetic behavior of an active replisome when it meets a nucleoprotein blockage3, as well as the mechanistic details of the replisome itself4,5. Current understanding of the repair of replication is generally undertaken with UV as the damaging agent and studied using plasmid DNA in vivo6-8. While the proteins that may be involved in repair of DNA after it encounters an in vivo nucleoprotein block are generally understood from these studies, whether there are variations in the molecular events within the repair pathways owing to the distinct cause in the replication block is still yet to be determined.
Here, we describe a system that allows a nucleoprotein block to be established in a specific location of the chromosome using a Fluorescent Repressor Operator System (FROS). We utilize a strain of E. coli that has had an array of 240 tetO sites incorporated into the chromosome9. Each tetO site within the array has a 10 bp random sequence flanking it to increase the stability of the array by preventing RecA-mediated recombination within the array. This array, and variations of it, were originally used to understand E. coli chromosome dynamics10,11 but were then adapted to prevent in vivo replication12. The array has been found to be stably maintained and to block close to 100% of replication forks when bound by TetR10,12. The use of the similar lacO array in vitro has found as few as 22 sites were sufficient to block 90% of replication, although this shorter array was less effective in vivo13. To adapt the array to create a nucleoprotein blockage, the repressor protein must be highly overproduced under optimized conditions where it then binds to the array to create a roadblock. The formation of the blockage, and its subsequent release, can be monitored through the use of fluorescence microscopy if a fluorescently tagged variant of the Tet repressor is used. The status of replication in each cell is indicated by the number of foci seen, where a single focal point means only one copy of the array is present within the cell and multiple foci are indicative of active replication. This active replication is enabled when the nucleoprotein blockage is reversed by the addition of the gratuitous inducer that decreases the binding affinity of TetR for the operator site sufficiently for the replisome to proceed through the array. The repressor protein is still able to bind to the DNA with high enough affinity that the now multiple copies of the array can be visualized.
More intricate details of the events at the nucleoprotein blockage can be discovered using neutral-neutral two-dimensional agarose gel electrophoresis and Southern hybridization14-16. These techniques allow the analysis of DNA structures across the population. The replication intermediates that are formed during the event, and potentially remain unrepaired, can be visualized. By varying the restriction enzyme and probe utilized, the intermediates can be visualized not only in the array region but also upstream of the array when the replication fork regresses17,18. The regression takes place subsequent to the replisome dissociation; the leading and lagging nascent strands separate from the template strands and anneal to each other as the template strands concurrently re-anneal resulting in a four-way DNA structure (a Holliday junction).
Using this system it has been shown that the replication fork is not stable when it encounters this block18. In addition, temperature sensitive derivatives of replisome components can be utilized to prevent reloading of the replication fork once it has collapsed. Once a block is established, the strain can be shifted to a non-permissive temperature to ensure a synchronous deactivation of the replisome and a controlled prevention of reloading. This temperature-induced deactivation ensures all of the forks within the population have collapsed at a given time and allows the assessment of what happens when the replisome collapses, how the DNA is processed, and what is required to restart the process of DNA replication.
An advantage of the system described here is that the nucleoprotein block is fully reversible; therefore, the ability of the cells to recover from the nucleoprotein block is able to be followed. The addition of anhydrotetracycline to the cells will relieve the tight binding of the repressor, allowing a replication fork to proceed through and the cell to regain viability. The relief of the blockage can be visualized by neutral-neutral two-dimensional agarose gel electrophoresis after 5 min, and by microscopy within 10 min. Furthermore, viability analysis can reveal the ability of the strain to recover from the replication blockage and continue to proliferate.
By altering the genetic background of the strains used in the experimental procedure described here, the repair pathways for this type of blockage can be elucidated.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Tryptone</td>
			<td>Sigma-Aldrich</td>
			<td>16922</td>
			<td>Growth media component</td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>VWR</td>
			<td>27810.364</td>
			<td>Growth media component</td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>Sigma-Aldrich</td>
			<td>92144</td>
			<td>Growth media component</td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Sigma-Aldrich</td>
			<td>P9791</td>
			<td>Growth media component; Potassium buffer component</td>
		</tr>
		<tr>
			<td>Potassium phosphate dibasic</td>
			<td>Sigma-Aldrich</td>
			<td>P3786</td>
			<td>Growth media component; Potassium buffer component</td>
		</tr>
		<tr>
			<td>L-Arabinose</td>
			<td>Sigma-Aldrich</td>
			<td>A3256</td>
			<td>For induction of TetR-YFP production</td>
		</tr>
		<tr>
			<td>Anhydrotetracycline hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>37919</td>
			<td>Release of replication bloackage</td>
		</tr>
		<tr>
			<td>Axioskop 2 Fluorescence microscope</td>
			<td>Zeiss</td>
			<td>452310</td>
			<td>Visualization of cells</td>
		</tr>
		<tr>
			<td>eYFP filter set</td>
			<td>Chroma Technology</td>
			<td>41028</td>
			<td>Visualization of YFP</td>
		</tr>
		<tr>
			<td>CCD camera</td>
			<td>Hamamatsu</td>
			<td>Orca-AG</td>
			<td>Visualization of cells</td>
		</tr>
		<tr>
			<td>MetaMorph&#160; Software (Molecular Devices)</td>
			<td>SDR Scientific</td>
			<td>31282</td>
			<td>Version 7.8.0.0 used in the preparation of this manuscript</td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Bioline</td>
			<td>BIO-41025</td>
			<td>For agarose plugs and gel electrophoresis</td>
		</tr>
		<tr>
			<td>Original Glass Water Repellent (Rain-X)</td>
			<td>Autobarn</td>
			<td>DIO1470</td>
			<td>For agarose plug manufacture</td>
		</tr>
		<tr>
			<td>TRIS</td>
			<td>VWR</td>
			<td>VWRC103157P</td>
			<td>TE, TBE buffer component</td>
		</tr>
		<tr>
			<td>Ethylene diaminetetraacetic acid</td>
			<td>Ajax Finechem</td>
			<td>AJA180</td>
			<td>0.5 M EDTA disodium salt solution adjusted to pH 8.0 with NaOH.</td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma-Aldrich</td>
			<td>S2002</td>
			<td>Bacteriostatic agent</td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td>Sigma-Aldrich</td>
			<td>258148</td>
			<td>TE buffer component</td>
		</tr>
		<tr>
			<td>Sodium deoxycholate</td>
			<td>Sigma-Aldrich</td>
			<td>D6750</td>
			<td>Cell lysis buffer component</td>
		</tr>
		<tr>
			<td>N-Lauroylsarcosine sodium salt (Sarkosyl)</td>
			<td>Sigma-Aldrich</td>
			<td>L5125</td>
			<td>Cell lysis and ESP buffer component</td>
		</tr>
		<tr>
			<td>Rnase A</td>
			<td>Sigma-Aldrich</td>
			<td>R6513</td>
			<td>Cell lysis buffer component</td>
		</tr>
		<tr>
			<td>Lysozyme</td>
			<td>Amresco</td>
			<td>6300</td>
			<td>Cell lysis buffer component</td>
		</tr>
		<tr>
			<td>Proteinase K</td>
			<td>Amresco</td>
			<td>AM0706</td>
			<td>ESP buffer component</td>
		</tr>
		<tr>
			<td>Sub-Cell Model 192 Cell</td>
			<td>BioRad</td>
			<td>1704507</td>
			<td>Electrophoresis system</td>
		</tr>
		<tr>
			<td>UV transilluminator 2000</td>
			<td>BioRad</td>
			<td>1708110</td>
			<td>Visualization of DNA</td>
		</tr>
		<tr>
			<td>Ethidium Bromide</td>
			<td>BioRad</td>
			<td>1610433</td>
			<td>Visualization of DNA</td>
		</tr>
		<tr>
			<td>Boric acid</td>
			<td>VWR</td>
			<td>PROL20185.360</td>
			<td>TBE component</td>
		</tr>
		<tr>
			<td>Hybond-XL nylon memrbane</td>
			<td>Amersham</td>
			<td>RPN203S</td>
			<td>Zeta-Probe Memrbane (BioRad 1620159) can also be used</td>
		</tr>
		<tr>
			<td>3MM Whatman chromatography paper</td>
			<td>GE Healthcare Life Sciences</td>
			<td>3030690</td>
			<td>Southern blotting</td>
		</tr>
		<tr>
			<td>HL-2000 Hybrilinker</td>
			<td>UVP</td>
			<td>95-0031-01/02</td>
			<td>Crosslinking of DNA and hybridization</td>
		</tr>
		<tr>
			<td>Deoxyribonucleic acid from salmon sperm</td>
			<td>Sigma-Aldrich</td>
			<td>31149</td>
			<td>Hybridization buffer component</td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td>Denaturation buffer component</td>
		</tr>
		<tr>
			<td>Trisodium citrate dihydrate</td>
			<td>VWR</td>
			<td>PROL27833.363</td>
			<td>Transfer buffer</td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulphate (SDS)</td>
			<td>Amresco</td>
			<td>227</td>
			<td>Wash buffer component</td>
		</tr>
		<tr>
			<td>Bovine serum albumin</td>
			<td>Sigma-Aldrich</td>
			<td>A7906</td>
			<td>Hybridization buffer component</td>
		</tr>
		<tr>
			<td>Random Hexamer Primers</td>
			<td>Bioline</td>
			<td>BIO-38028</td>
			<td></td>
		</tr>
		<tr>
			<td>Klenow fragment</td>
			<td>New England BioLabs</td>
			<td>M0212L</td>
			<td></td>
		</tr>
		<tr>
			<td>dNTP Set</td>
			<td>Bioline</td>
			<td>BIO-39025</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenosine 5&#8217;-triphosphate-32P-ATP</td>
			<td>PerkinElmer</td>
			<td>BLU502A</td>
			<td></td>
		</tr>
		<tr>
			<td>Storage Phosphor Screen</td>
			<td>GE Healthcare Life Sciences</td>
			<td>GEHE28-9564-76</td>
			<td>BAS-IP MS 3543 E multipurpose standard 35x43cm screen</td>
		</tr>
		<tr>
			<td>Typhoon FLA 7000</td>
			<td>GE Healthcare Life Sciences</td>
			<td>28-9558-09</td>
			<td>Visualization of blot</td>
		</tr>
		<tr>
			<td>Hybridization bottle</td>
			<td>UVP</td>
			<td>07-0194-02</td>
			<td>35 x 300mm</td>
		</tr>
	</tbody>
</table>

inducing a site specific replication blockage in e. coli using a fluorescent repressor operator system

Obstacles present on DNA, including tightly-bound proteins and various lesions, can severely inhibit the progression of the cell&#39;s replication machinery. The stalling of a replisome can lead to its dissociation from the chromosome, either in part or its entirety, leading to the collapse of the replication fork. The recovery from this collapse is a necessity for the cell to accurately complete chromosomal duplication and subsequently divide. Therefore, when the collapse occurs, the cell has evolved diverse mechanisms that take place to restore the DNA fork and allow replication to be completed with high fidelity. Previously, these replication repair pathways in bacteria have been studied using UV damage, which has the disadvantage of not being localized to a known site. This manuscript describes a system utilizing a Fluorescence Repressor Operator System (FROS) to create a site-specific protein block that can induce the stalling and collapse of replication forks in Escherichia coli. Protocols detail how the status of replication can be visualized in single living cells using fluorescence microscopy and DNA replication intermediates can be analyzed by 2-dimensional agarose gel electrophoresis. Temperature sensitive mutants of replisome components (e.g. DnaBts) can be incorporated into the system to induce a synchronous collapse of the replication forks. Furthermore, the roles of the recombination proteins and helicases that are involved in these processes can be studied using genetic knockouts within this system.

The FROS is an inducible, site-specific nucleoprotein block that enables replication intermediates to be visualized in living cells12,18. A general experimental design for sampling cells is illustrated in Figure 1. The timing of the sampling and variations in genetic background make this a versatile system for studying the repair of such a block. The schematic illustrates how temperature sensitive mutants, such as dnaBts and dnaCts that have b...

Watch this Scientific Journal Video about Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System at JoVE.com

Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System

We describe here a system utilizing a site-specific, reversible in vivo protein block to stall and collapse replication forks in Escherichia coli. The establishment of the replication block is evaluated by fluorescence microscopy and neutral-neutral 2-dimensional agarose gel electrophoresis is used to visualize replication intermediates.

Inducing a Site Specific Replication Blockage in E. coli Using a Fluorescent Repressor Operator System

Obstacles present on DNA, including tightly-bound proteins and various lesions, can severely inhibit the progression of the cell&#39;s replication ...

Research

JoVE Journal

Biology

Transformation of Plasmid DNA into E. coli Using the Heat Shock Method

Transformation of plasmid DNA into E. coli using the heat shock method is a basic technique of molecular biology. It consists of inserting a foreign ...

Principles of Site-Specific Recombinase (SSR) Technology

Principles of Site-Specific Recombinase SSR Technology

Site-specific recombinase (SSR) technology allows the manipulation of gene structure to explore gene function and has become an integral tool of molecular ...

Visualization of UV-induced Replication Intermediates in E. coli using Two-dimensional Agarose-gel Analysis

Visualization of UV-induced Replication Intermediates in E. coli using Two-dimensional Agarose-gel Analysis

Inaccurate replication in the presence of DNA damage is responsible for the majority of cellular rearrangements and mutagenesis observed in all cell types ...

Mutagenesis and Functional Selection Protocols for Directed Evolution of Proteins in E. coli

Mutagenesis and Functional Selection Protocols for Directed Evolution of Proteins in E. coli

The efficient generation of genetic diversity represents an invaluable molecular tool that can be used to label DNA synthesis, to create unique molecular ...

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

 
Symbioses, the living together of two or more organisms, are widespread throughout all kingdoms of life. As two of the most ubiquitous organisms on ...

The Logic, Experimental Steps, and Potential of Heterologous Natural Product Biosynthesis Featuring the Complex Antibiotic Erythromycin A Produced Through E. coli

The Logic, Experimental Steps, and Potential of Heterologous Natural Product Biosynthesis Featuring the Complex Antibiotic Erythromycin A Produced Through E. coli

The heterologous production of complex natural products is an approach designed to address current limitations and future possibilities.  It is ...

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

Using Caenorhabditis elegans as a Model System to Study Protein Homeostasis in a Multicellular Organism

The folding and assembly of proteins is essential for protein function, the long-term health of the cell, and longevity of the organism. Historically, the ...

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

Green Fluorescent Protein-based Expression Screening of Membrane Proteins in Escherichia coli

The production of recombinant membrane proteins for structural and functional studies remains technically challenging due to low levels of expression and ...

Detection of Intracellular Gene Expression in Live Cells of Murine, Human and Porcine Origin Using Fluorescence-labeled Nanoparticles

The reprogramming of somatic cells to induced pluripotent stem cells (iPS) has successfully been performed in different mammalian species including mouse, ...

Validation of a Mouse Model to Disrupt LINC Complexes in a Cell-specific Manner

Nuclear migration and anchorage within developing and adult tissues relies heavily upon large macromolecular protein assemblies called LInkers of the ...