Name: dna polymerase activity assay using near-infrared fluorescent labeled dna visualized by acrylamide gel electrophoresis
Uploaded: 2017-10-06T15:00:00.000+00:00
Duration: 7 min 38 s
Description: Watch this Scientific Journal Video about DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis at JoVE.com

This work was supported by the Research Corporation for Scientific Advancement (Cottrell College Scholar Award #22548) and by TriLink Biotechnologies (ResearchReward Grant #G139).&#160;

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selection+of+2'-deoxy-2'-fluoroarabinonucleotide+(FANA)+aptamers+that+bind+HIV-1+reverse+transcriptase+with+picomolar+affinity.">Selection of 2'-deoxy-2'-fluoroarabinonucleotide (FANA) aptamers that bind HIV-1 reverse transcriptase with picomolar affinity.</a> Nucleic Acids Res. 43 (20), 9587-9599 (2015).</li><li>Schultz, H. J., 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=Taq+DNA+Polymerase+Mutants+and+2'-Modified+Sugar+Recognition.">Taq DNA Polymerase Mutants and 2'-Modified Sugar Recognition.</a> Biochemistry. 54 (38), 5999-6008 (2015).</li><li>Rosenblum, S. 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=Design+and+discovery+of+new+combinations+of+mutant+DNA+polymerases+and+modified+DNA+substrates.">Design and discovery of new combinations of mutant DNA polymerases and modified DNA substrates.</a> Chembiochem. 18 (8), 816-823 (2017).</li><li>Creighton, S., Goodman, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gel+kinetic+analysis+of+DNA+polymerase+fidelity+in+the+presence+of+proofreading+using+bacteriophage+T4+DNA+polymerase.">Gel kinetic analysis of DNA polymerase fidelity in the presence of proofreading using bacteriophage T4 DNA polymerase.</a> J Biol Chem. 270 (9), 4759-4774 (1995).</li><li>Joyce, C. M., Benkovic, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+polymerase+fidelity:+kinetics,+structure,+and+checkpoints.">DNA polymerase fidelity: kinetics, structure, and checkpoints.</a> Biochemistry. 43 (45), 14317-14324 (2004).</li><li>Leconte, A. M., 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=Discovery,+characterization,+and+optimization+of+an+unnatural+base+pair+for+expansion+of+the+genetic+alphabet.">Discovery, characterization, and optimization of an unnatural base pair for expansion of the genetic alphabet.</a> J Am Chem Soc. 130 (7), 2336-2343 (2008).</li><li>Sanger, F., Nicklen, S., Coulson, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+sequencing+with+chain-terminating+inhibitors.">DNA sequencing with chain-terminating inhibitors.</a> Proc Natl Acad Sci U S A. 74 (12), 5463-5467 (1977).</li><li>Karger, B. L., Guttman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+Sequencing+by+Capillary+Electrophoresis.">DNA Sequencing by Capillary Electrophoresis.</a> Electrophoresis. 30 (Suppl 1), S196-S202 (2009).</li><li>Lawyer, F. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mutant+of+DNA+polymerase+I+(Klenow+fragment)+with+reduced+fidelity.">A mutant of DNA polymerase I (Klenow fragment) with reduced fidelity.</a> Biochemistry. 30 (3), 804-813 (1991).</li><li>Shendure, J., Ji, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Next-generation+DNA+sequencing.">Next-generation DNA sequencing.</a> Nat Biotechnol. 26 (10), 1135-1145 (2008).</li><li>Larsen, A. 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The authors have nothing to disclose.

Here, we have described an assay to characterize the DNA polymerase-mediated synthesis of M-DNA. By using near-infrared labeled DNA primers, and using denaturing polyacrylamide gel electrophoresis to resolve differently sized oligonucleotides, we can obtain single nucleotide resolution on oligonucleotides, enabling precise measurement of synthesis. These approaches can be used to either measure the overall activity of the enzyme (section 2.1) or to measure the Michaelis-Menten parameters of individual steps (note followi...

DNA polymerases perform accurate and efficient DNA synthesis and are essential to maintaining genome integrity. The ability to synthesize hundreds of nucleotides per second without making errors also makes DNA polymerases essential tools in molecular biology and biotechnology. However, these properties also limit the applications for M-DNA substrates; generally speaking, natural DNA polymerases cannot synthesize many potentially valuable M-DNA substrates, likely due to the high selective pressure against using non-standard substrates in vivo. Many groups have developed directed evolution approaches to generate mutant DNA polymerases capable of M-DNA synthesis1a,2,3,4,5; these efforts have expanded the biotechnological utility of DNA6,7,8.
To evaluate the ability of mutant DNA polymerases to synthesize M-DNA, we9,10, and others11,12,13 typically use in vitro measurements of DNA polymerase activity, which are described in this manuscript. In these experiments, DNA polymerases are co-incubated with a labeled primer/template duplex and nucleoside triphosphate substrates; the products are evaluated by gel electrophoresis. Depending on the specific experimental question, mutant DNA polymerases, modified primers, modified templates, or modified nucleoside triphosphates can be used, enabling the systematic biochemical evaluation of the mutant enzyme activity.
Historically, these assays have relied on a 5&#39; radioactive label to track DNA synthesis; most commonly, 32P and 33P have been used; typically, labeling is achieved using T4 polynucleotide kinase11. However, due to the finite lifetime and relatively high cost of radioactive labels and their safe disposal, our group instead uses a synthetic 5&#39; near-infrared fluorophore labeled DNA. Using a relatively low cost near-infrared gel imager, we have observed similar detection limits to prior studies using radioactive labels (unpublished results). We have successfully reproduced past observations9, and we have not observed any large quantitative difference with previously measured rate constants (unpublished results).
To analyze the size of DNA, and thus, the extent of DNA synthesis, we rely on polyacrylamide gel electrophoresis methods developed originally for Sanger sequencing14 before the advent of capillary electrophoresis15. The distance of separation or mobility can be used as a measurement of molecular weight; large format, vertical polyacrylamide gels can achieve single nucleotide resolution, enabling quantitative observation of DNA oligonucleotides of varying lengths.
Collectively, these experiments are a robust method for polymerase characterization. Due to the time sensitive nature of the reactions, preparation and care is necessary to achieve reproducible results. Further, while the acrylamide gel is a highly effective way to measure DNA synthesis, as well as numerous other DNA modifying reactions, with single nucleotide resolution, it can be technically challenging. The protocol here will hopefully enable users to perform these experiments while avoiding the most common mistakes.

<table><tbody><tr><td>Tris HCl</td><td>Promega</td><td>H5123</td><td></td></tr><tr><td>Tris Base</td><td>Promega</td><td>H5131</td><td></td></tr><tr><td>MgCl&lt;sub&gt;2&lt;/sub&gt;</td><td>Fisher Scientific</td><td>BP214-500</td><td></td></tr><tr><td>Acetylated BSA</td><td>Promega</td><td>PR-R3961</td><td></td></tr><tr><td>KCl</td><td>Sigma</td><td>P4504</td><td></td></tr><tr><td>Dithiothreitol (i.e. DTT)</td><td>Research Products International</td><td>D11000</td><td></td></tr><tr><td>Ethylenediaminetetraacetic acid (i.e. EDTA) (0.5M solution)</td><td>Sigma</td><td>03690-100mL</td><td></td></tr><tr><td>Glycerol</td><td>Sigma</td><td>G5516</td><td></td></tr><tr><td>Formamide</td><td>Acros</td><td>AC42374-5000</td><td></td></tr><tr><td>Orange G</td><td>Sigma Aldrich</td><td>O3756</td><td></td></tr><tr><td>Bromophenol blue</td><td>Fisher Scientific</td><td>50-701-6973</td><td></td></tr><tr><td>dNTPs</td><td>Fisher Scientific</td><td>FERR0191</td><td></td></tr><tr><td>M-dNTPs (riboNTPs)</td><td>Fisher Scientific</td><td>45-001-341 (343, 345, 347)</td><td></td></tr><tr><td>M-dNTPs (all other modified NTPs)</td><td>TriLink Biotechnologies</td><td>assorted</td><td></td></tr><tr><td>primer 1</td><td>IDT DNA / TriLink Biotechnologies</td><td>Custom Syntheses</td><td>We use the IR700 dye which can be purchased as a custom synthesis. We typically purchase the oligonucleotides HPLC purified. Sequence is 5&amp;rsquo;-dTAATACGACTCACTATAGGGAGA</td></tr><tr><td>template 1</td><td>IDT DNA / TriLink Biotechnologies</td><td>Custom Syntheses</td><td>We typically purchase the oligonucleotides HPLC purified. Sequence is 5&amp;rsquo;-dCGCTAGGACGGCATTGGATCAGTCTCCCTATAGTGAGTCGTATTA</td></tr><tr><td>Acrylamide</td><td>Research Products International</td><td>A11405</td><td>38.67% acrylamide and 1.33% bis-acrylamide</td></tr><tr><td>Tris/Borate/EDTA (TBE) solid</td><td>Research Products International</td><td>T22020</td><td></td></tr><tr><td>Urea ultrapure</td><td>Research Products International</td><td>U20200</td><td></td></tr><tr><td>Gel tape</td><td>CBS Scientific</td><td>GT-72-10</td><td></td></tr><tr><td>Large white spring clamp polypropylene</td><td>CBS Scientific</td><td>GPC-0001</td><td></td></tr><tr><td>Ammonium persulfate (APS)</td><td>Fisher Scientific</td><td>BP179</td><td></td></tr><tr><td>Tetramethylethylenediamine (TEMED)</td><td>Fisher Scientific</td><td>BP15020</td><td></td></tr><tr><td>0.75 mm spacers</td><td>CBS Scientific</td><td>SGS-20-0740A</td><td></td></tr><tr><td>33x42 Notched Glass Plate Set</td><td>CBS Scientific</td><td>SGP33-040A</td><td></td></tr><tr><td>Wedge plate separator</td><td>CBS Scientific</td><td>WPS-100</td><td></td></tr><tr><td>Comb for gel electrophoresis</td><td>CBS Scientific</td><td>SG33-0734</td><td></td></tr><tr><td>Gel electrophoresis rig</td><td>CBS Scientific</td><td>SG-400-33</td><td></td></tr><tr><td>ultrapure water</td><td></td><td></td><td>we use a Milli-Q system from Millipore</td></tr><tr><td>DNA polymerases</td><td></td><td></td><td>we prepare these in our laboratory using published protocols.</td></tr></tbody></table>

dna polymerase activity assay using near-infrared fluorescent labeled dna visualized by acrylamide gel electrophoresis

For any enzyme, robust, quantitative methods are required for characterization of both native and engineered enzymes. For DNA polymerases, DNA synthesis can be characterized using an in vitro DNA synthesis assay followed by polyacrylamide gel electrophoresis. The goal of this assay is to quantify synthesis of both natural DNA and modified DNA (M-DNA). These approaches are particularly useful for resolving oligonucleotides with single nucleotide resolution, enabling observation of individual steps during enzymatic oligonucleotide synthesis. These methods have been applied to the evaluation of an array of biochemical and biophysical properties such as the measurement of steady-state rate constants of individual steps of DNA synthesis, the error rate of DNA synthesis, and DNA binding affinity. By using modified components including, but not limited to, modified nucleoside triphosphates (NTP), M-DNA, and/or mutant DNA polymerases, the relative utility of substrate-DNA polymerase pairs can be effectively evaluated. Here, we detail the assay itself, including the changes that must be made to accommodate nontraditional primer DNA labeling strategies such as near-infrared fluorescently labeled DNA. Additionally, we have detailed crucial technical steps for acrylamide gel pouring and running, which can often be technically challenging.

A successful polyacrylamide gel analysis of a qualitative characterization of overall activity (described in section 2.1, Figure 1) and of steady-state kinetics (described in the note at conclusion of section 2.1, Figure 2) are shown. An unsuccessful polyacrylamide gel analysis is also shown (Figure 3).
Note that no commercially available l...

Watch this Scientific Journal Video about DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis at JoVE.com

DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis

This protocol describes the characterization of DNA polymerase synthesis of modified DNA through observation of changes to near-infrared fluorescently labeled DNA using gel electrophoresis and gel imaging. Acrylamide gels are used for high resolution imaging of the separation of short nucleic acids, which migrate at different rates depending on size.

For any enzyme, robust, quantitative methods are required for characterization of both native and engineered enzymes. For DNA polymerases, DNA synthesis ...

dna-polymerase-activity-assay-using-near-infrared-fluorescent-labeled

Research

JoVE Journal

Biochemistry

14.1K Views.  W.M. Keck Science Department of Claremont Mckenna, Pitzer, and Scripps College. This protocol describes the characterization of DNA polymerase synthesis of modified DNA through observation of changes to near-infrared fluorescently labeled DNA using gel electrophoresis and gel imaging. Acrylamide gels are used for high resolution imaging of the separation of short nucleic acids, which migrate at different rates depending on size.

Video: DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis

An Optimized Protocol for Electrophoretic Mobility Shift Assay Using Infrared Fluorescent Dye-labeled Oligonucleotides

Electrophoretic Mobility Shift Assays (EMSA) are an instrumental tool to characterize the interactions between proteins and their target DNA sequences. Radioactivity has been the predominant method of DNA labeling in EMSAs. However, recent advances in fluorescent dyes and scanning methods have prompted the use of fluorescent tagging of DNA as an alternative to radioactivity for the advantages of easy handling, saving time, reducing cost, and improving safety. We have recently used fluorescent EMSA (fEMSA) to successfully address an important biological question. Our fEMSA analysis provides mechanistic insight into the effect of a missense mutation, G73E, in the highly conserved HMG transcription factor SOX-2 on olfactory neuron type diversification. We found that mutant SOX-2G73E protein alters specific DNA binding activity, thereby causing olfactory neuron identity transformation. Here, we present an optimized and cost-effective step-by-step protocol for fEMSA using infrared fluorescent dye-labeled oligonucleotides containing the LIM-4/SOX-2 adjacent target sites and purified SOX-2 proteins (WT and mutant SOX-2G73E proteins) as a biological example.

We describe here an optimized protocol of fluorescent Electrophoretic Mobility Shift Assays (fEMSA) using purified SOX-2 proteins together with infrared fluorescent dye-labeled DNA probes as a case study to tackle an important biological question.

Electrophoretic Mobility Shift Assays (EMSA) are an instrumental tool to characterize the interactions between proteins and their target DNA sequences. ...

DNA Staining Method Based on Formazan Precipitation Induced by Blue Light Exposure

DNA staining methods are very important for biomedical research. We designed a simple method that allows DNA visualization to the naked eye by the formation of a colored precipitate. It works by soaking the acrylamide or agarose DNA gel in a solution of 1x (equivalent to 2.0 &#181;M) SYBR Green I (SG I) and 0.20 mM nitro blue tetrazolium that produces a purple precipitate of formazan when exposed to sunlight or specifically blue light. Also, DNA recovery tests were performed using an ampicillin resistant plasmid in an agarose gel stained with our method. A larger number of colonies was obtained with our method than with traditional staining using SG I with ultraviolet illumination. The described method is fast, specific, and non-toxic for DNA detection, allowing visualization of biomolecules to the "naked eye" without a transilluminator, and is inexpensive and appropriate for field use. For these reasons, our new DNA staining method has potential benefits to both research and industry.

This method allows selective staining and quantification of DNA in gels by soaking the gel in a SYBR Green I/Nitro Blue Tetrazolium solution and then exposing it to sunlight or a blue light source. This produces a visible precipitate and requires almost no equipment, making it ideal for field use.

DNA staining methods are very important for biomedical research. We designed a simple method that allows DNA visualization to the naked eye by the ...

Nonradioactive Assay to Measure Polynucleotide Phosphorylation of Small Nucleotide Substrates

Polynucleotide kinases (PNKs) are enzymes that catalyze the phosphorylation of the 5&#39; hydroxyl end of DNA and RNA oligonucleotides. The activity of PNKs can be quantified using direct or indirect approaches. Presented here is a direct, in vitro approach to measure PNK activity that relies on a fluorescently-labeled oligonucleotide substrate and polyacrylamide gel electrophoresis. This approach provides resolution of the phosphorylated products while avoiding the use of radiolabeled substrates. The protocol details how to set up the phosphorylation reaction, prepare and run large polyacrylamide gels, and quantify the reaction products. The most technically challenging part of this assay is pouring and running the large polyacrylamide gels; thus, important details to overcome common difficulties are provided. This protocol was optimized for Grc3, a PNK that assembles into an obligate pre-ribosomal RNA processing complex with its binding partner, the Las1 nuclease. However, this protocol can be adapted to measure the activity of other PNK enzymes. Moreover, this assay can also be modified to determine the effects of different components of the reaction, such as the nucleoside triphosphate, metal ions, and oligonucleotides.

This protocol describes a nonradioactive assay to measure kinase activity of polynucleotide kinases (PNKs) on small DNA and RNA substrates.

Polynucleotide kinases (PNKs) are enzymes that catalyze the phosphorylation of the 5&#39; hydroxyl end of DNA and RNA oligonucleotides. The activity of ...

Quantifying DNA Double Strand Break Repair with Nanoluciferase Reporter Assays

Assessment of DNA Double Strand Break Repair Activity Using High-throughput and Quantitative Luminescence-Based Reporter Assays

The repair of DNA double strand breaks (DSBs) is crucial for the maintenance of genome stability and cell viability. DSB repair (DSBR) in cells is mediated through several mechanisms: homologous recombination (HR), non-homologous end joining (NHEJ), microhomology-mediated end joining (MMEJ), and single strand annealing (SSA). Cellular assays are essential to measure the proficiency and modulation of these pathways in response to various stimuli.
Here, we present a suite of extrachromosomal reporter assays that each measure the reconstitution of a nanoluciferase reporter gene by one of the four major DSBR pathways in cells. Upon transient transfection into cells of interest, repair of pathway-specific reporter substrates can be measured in under 24 h by the detection of Nanoluciferase (NanoLuc) luminescence.
These robust assays are quantitative, sensitive, titratable, and amenable to a high-throughput screening format. These properties provide broad applications in DNA repair research and drug discovery, complementing the currently available toolkit of cellular DSBR assays.

Author Spotlight: Developing Novel Anticancer Therapeutics Targeting the DNA Damage Response

We present protocols for the assessment of double strand break repair pathway proficiency in cells using a suite of luminescence-based extrachromosomal reporter substrates.

The repair of DNA double strand breaks (DSBs) is crucial for the maintenance of genome stability and cell viability. DSB repair (DSBR) in cells is ...

Cancer Research

Precision DNAzyme Nanomachines for Discriminative RNA and DNA Analysis

DNAzyme 10-23 - Based Nanomachines for Nucleic Acid Recognition

DNAzyme-based nanomachines (DNM) for the detection of DNA and RNA sequences (analytes) are multifunctional structures made of oligonucleotides. Their functions include tight analyte binding, highly selective analyte recognition, fluorescent signal amplification by multiple catalytic cleavages of a fluorogenic reporter substrate, and fluorogenic substrate attraction for an increase in sensor response. Functional units are attached to a common DNA scaffold for their cooperative action. The RNA-cleaving 10-23 DNMs feature&#160;improved sensitivity in comparison with non-catalytic hybridization probes. The stability of the DNM and the increased chances of substrate recognition are provided&#160;by a double-stranded DNA fragment,&#160;a tile. DNM can differentiate two analytes with a single nucleotide difference in a folded RNA and a double-stranded DNA and detect analytes at concentrations ~1000 times lower than other protein-free hybridization probes. This article presents the concept behind the diagnostic potential of DNA-nanomachine activity and overviews DNM design, assembly, and application&#160;in nucleic acid detection assays.

Author Spotlight: Advancements in DNA Nanosensors &#8211; Addressing Sensitivity and Selectivity Challenges in Molecular Detection

The DNAzyme-based nanomachines can be used for highly selective and sensitive detection of nucleic acids. This article describes a detailed protocol for the design of DNAzyme-based nanomachines with a 10-23 core using free software and their application in the detection of an Epstein-Barr virus fragment as an example.

DNAzyme-based nanomachines (DNM) for the detection of DNA and RNA sequences (analytes) are multifunctional structures made of oligonucleotides. Their ...

Assays for DNA Enzymes Using Synthetic Oligonucleotides

Using Modified Synthetic Oligonucleotides to Assay Nucleic Acid-Metabolizing Enzymes

The availability of a range of modified synthetic oligonucleotides from commercial vendors has allowed the development of sophisticated assays to characterize diverse properties of nucleic acid metabolizing enzymes that can be run in any standard molecular biology lab. The use of fluorescent labels has made these methods accessible to researchers with standard PAGE electrophoresis equipment and a fluorescent-enabled imager, without using radioactive materials or requiring a lab designed for the storage and preparation of radioactive materials, i.e., a Hot Lab. The optional addition of standard modifications such as phosphorylation can simplify assay setup, while the specific incorporation of modified nucleotides that mimic DNA damages or intermediates can be used to probe specific aspects of enzyme behavior. Here, the design and execution of assays to interrogate several aspects of DNA processing by enzymes using commercially available synthetic oligonucleotides are demonstrated. These include the ability of ligases to join or nucleases to degrade different DNA and RNA hybrid structures, differential cofactor usage by the DNA ligase, and evaluation of the DNA-binding capacity of enzymes. Factors to consider when designing synthetic nucleotide substrates are discussed, and a basic set of oligonucleotides that can be used for a range of nucleic acid ligase, polymerase, and nuclease enzyme assays are provided.

Author Spotlight: Characterizing Novel Enzymes from Extremophiles and Common Pathogens to Understand DNA Repair and Replication

Here, a protocol for assaying nucleic acid metabolizing enzymes is presented, using examples of ligase, nuclease, and polymerase enzymes. The assay utilizes fluorescently labeled and unlabeled oligonucleotides that can be combined to form duplexes mimicking RNA and/or DNA damages or pathway intermediates, allowing for the characterization of enzyme behavior.

The availability of a range of modified synthetic oligonucleotides from commercial vendors has allowed the development of sophisticated assays to ...

DNA-Tethered RNA Polymerase for Programmable In vitro Transcription and Molecular Computation

DNA nanotechnology enables programmable self-assembly of nucleic acids into user-prescribed shapes and dynamics for diverse applications. This work demonstrates that concepts from DNA nanotechnology can be used to program the enzymatic activity of the phage-derived T7 RNA polymerase (RNAP) and build scalable synthetic gene regulatory networks. First, an oligonucleotide-tethered T7 RNAP is engineered via expression of an N-terminally SNAP-tagged RNAP and subsequent chemical coupling of the SNAP-tag with a benzylguanine (BG)-modified oligonucleotide. Next, nucleic-acid strand displacement is used to program polymerase transcription on-demand. In addition, auxiliary nucleic acid assemblies can be used as &#34;artificial transcription factors&#34; to regulate the interactions between the DNA-programmed T7 RNAP with its DNA templates. This in vitro transcription regulatory mechanism can implement a variety of circuit behaviors such as digital logic, feedback, cascading, and multiplexing. The composability of this gene regulatory architecture facilitates design abstraction, standardization, and scaling. These features will enable the rapid prototyping of in vitro&#160;genetic devices for applications such as bio-sensing, disease detection, and data storage.

We describe the engineering of a novel DNA-tethered T7 RNA polymerase to regulate in vitro transcription reactions. We discuss the steps for protein synthesis and characterization, validate proof-of-concept transcriptional regulation, and discuss its applications in molecular computing, diagnostics, and molecular information processing.

DNA nanotechnology enables programmable self-assembly of nucleic acids into user-prescribed shapes and dynamics for diverse applications. This work ...

Bioengineering

A Fluorescence-based Exonuclease Assay to Characterize DmWRNexo, Orthologue of Human Progeroid WRN Exonuclease, and Its Application to Other Nucleases

WRN exonuclease is involved in resolving DNA damage that occurs either during DNA replication or following exposure to endogenous or exogenous genotoxins. It is likely to play a role in preventing accumulation of recombinogenic intermediates that would otherwise accumulate at transiently stalled replication forks, consistent with a hyper-recombinant phenotype of cells lacking WRN. In humans, the exonuclease domain comprises an N-terminal portion of a much larger protein that also possesses helicase activity, together with additional sites important for DNA and protein interaction. By contrast, in Drosophila, the exonuclease activity of WRN (DmWRNexo) is encoded by a distinct genetic locus from the presumptive helicase, allowing biochemical (and genetic) dissection of the role of the exonuclease activity in genome stability mechanisms. Here, we demonstrate a fluorescent method to determine WRN exonuclease activity using purified recombinant DmWRNexo and end-labeled fluorescent oligonucleotides. This system allows greater reproducibility than radioactive assays as the substrate oligonucleotides remain stable for months, and provides a safer and relatively rapid method for detailed analysis of nuclease activity, permitting determination of nuclease polarity, processivity, and substrate preferences.

Exonucleases play critical roles in ensuring genome stability. Loss of WRN exonuclease function results in premature aging. Studying substrates and other requirements of the nuclease in vitro can help elucidate its role in vivo. Here we demonstrate a rapid and reproducible fluorescence-based assay to measure its nuclease activity.

WRN exonuclease is involved in resolving DNA damage that occurs either during DNA replication or following exposure to endogenous or exogenous genotoxins. ...

Biology

Simple Bulk Readout of Digital Nucleic Acid Quantification Assays

Digital assays are powerful methods that enable detection of rare cells and counting of individual nucleic acid molecules. However, digital assays are still not routinely applied, due to the cost and specific equipment associated with commercially available methods. Here we present a simplified method for readout of digital droplet assays using a conventional real-time PCR instrument to measure bulk fluorescence of droplet-based digital assays.
We characterize the performance of the bulk readout assay using synthetic droplet mixtures and a droplet digital multiple displacement amplification (MDA) assay. Quantitative MDA particularly benefits from a digital reaction format, but our new method&#160;applies to any digital assay. For established digital assay protocols such as digital PCR, this method serves to speed up and simplify assay readout.
Our bulk readout methodology brings the advantages of partitioned assays without the need for specialized readout instrumentation. The principal limitations of the bulk readout methodology are reduced dynamic range compared with droplet-counting platforms and the need for a standard sample, although the requirements for this standard are less demanding than for a conventional real-time experiment. Quantitative whole genome amplification (WGA) is used to test for contaminants in WGA reactions and is the most sensitive way to detect the presence of DNA fragments with unknown sequences, giving the method great promise in diverse application areas including pharmaceutical quality control and astrobiology.

We describe an endpoint digital assay for quantifying nucleic acids with a simplified (analog) readout. We measure bulk fluorescence of droplet-based digital assays using a standard qPCR machine rather than specialized instrumentation and confirm our results by microscopy.

Digital assays are powerful methods that enable detection of rare cells and counting of individual nucleic acid molecules. However, digital assays are ...

Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes

The ability of proteins&#160;involved in eukaryotic DNA replication to&#160;overcome obstacles &#8212; such as protein and DNA &#39;roadblocks&#39;&#160;&#8212; is critical for ensuring faithful&#160;genome duplication.&#160;G-quadruplexes are higher-order nucleic acid structures that form in guanine-rich regions of DNA and have been shown to act as obstacles, interfering with genomic maintenance pathways. This study introduces a real-time, fluorescence microscopy-based method to observe DNA polymerase interactions with G-quadruplex structures. Short, primed DNA oligonucleotides containing a G-quadruplex were immobilized on functionalized glass coverslips within a microfluidic flow cell. Fluorescently labeled DNA polymerases were introduced, allowing their behavior and stoichiometry to be monitored over time. This approach enabled the observation of polymerase behavior as it was stalled by a G-quadruplex. Specifically, using fluorescently labeled yeast polymerase &#948;, it was found that upon encountering a G-quadruplex, the polymerase undergoes a continuous cycle of binding and unbinding. This single-molecule assay can be adapted to study interactions between various DNA-maintenance proteins and obstacles on the DNA substrate.

This protocol outlines a fluorescence microscopy-based single-molecule DNA replication assay, enabling real-time visualization of interactions between DNA polymerases and obstacles such as G-quadruplex structures.