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>
	<li>Ong, J. L., Loakes, D., Jaroslawski, S., Too, K., Holliger, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+evolution+of+DNA+polymerase,+RNA+polymerase+and+reverse+transcriptase+activity+in+a+single+polypeptide.">Directed evolution of DNA polymerase, RNA polymerase and reverse transcriptase activity in a single polypeptide.</a> J Mol Biol. 361 (3), 537-550 (2006).</li><li>Chen, T., Romesberg, F. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+polymerase+evolution.">Directed polymerase evolution.</a> FEBS letters. 588 (2), 219-229 (2014).</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=Directed+evolution+of+DNA+polymerases+for+next-generation+sequencing.">Directed evolution of DNA polymerases for next-generation sequencing.</a> Angew Chem Int Ed Engl. 49 (34), 5921-5924 (2010).</li><li>Xia, G., 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=Directed+evolution+of+novel+polymerase+activities:+mutation+of+a+DNA+polymerase+into+an+efficient+RNA+polymerase.">Directed evolution of novel polymerase activities: mutation of a DNA polymerase into an efficient RNA polymerase.</a> Proc Natl Acad Sci U S A. 99 (10), 6597-6602 (2002).</li><li>Chen, 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=Evolution+of+thermophilic+DNA+polymerases+for+the+recognition+and+amplification+of+C2'-modified+DNA.">Evolution of thermophilic DNA polymerases for the recognition and amplification of C2'-modified DNA.</a> Nat Chem. 8 (6), 556-562 (2016).</li><li>Thirunavukarasu, D., Chen, T., Liu, Z., Hongdilokkul, N., Romesberg, F. E. <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'-Fluoro-Modified+Aptamers+with+Optimized+Properties.">Selection of 2'-Fluoro-Modified Aptamers with Optimized Properties.</a> J Am Chem Soc. 139 (8), 2892-2895 (2017).</li><li>Taylor, A. I., 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=Catalysts+from+synthetic+genetic+polymers.">Catalysts from synthetic genetic polymers.</a> Nature. 518 (7539), 427-430 (2015).</li><li>Alves Ferreira-Bravo, I., Cozens, C., Holliger, P., DeStefano, J. 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. C., 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-level+expression,+purification,+and+enzymatic+characterization+of+full-length+Thermus+aquaticus+DNA+polymerase+and+a+truncated+form+deficient+in+5'+to+3'+exonuclease+activity.">High-level expression, purification, and enzymatic characterization of full-length Thermus aquaticus DNA polymerase and a truncated form deficient in 5' to 3' exonuclease activity.</a> PCR Methods Appl. 2 (4), 275-287 (1993).</li><li>Lawyer, F. C., 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=Isolation,+characterization,+and+expression+in+Escherichia+coli+of+the+DNA+polymerase+gene+from+Thermus+aquaticus.">Isolation, characterization, and expression in Escherichia coli of the DNA polymerase gene from Thermus aquaticus.</a> J Biol Chem. 264 (11), 6427-6437 (1989).</li><li>Carroll, S. S., Cowart, 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=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. C., 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=A+general+strategy+for+expanding+polymerase+function+by+droplet+microfluidics.">A general strategy for expanding polymerase function by droplet microfluidics.</a> Nat Commun. 7, 11235 (2016).</li><li>Cozens, C., 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=Enzymatic+Synthesis+of+Nucleic+Acids+with+Defined+Regioisomeric+2'-5'+Linkages.">Enzymatic Synthesis of Nucleic Acids with Defined Regioisomeric 2'-5' Linkages.</a> Angew Chem Int Ed Engl. 54 (51), 15570-15573 (2015).</li></ol>

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 following step 2.1). Our lab has recently used these to both characterize previously evolved enzymes9 as well as rationally engineered enzymes10.
Our assays described here differ from prior methods in their use of a non-radioactive DNA label. Historically, radioactivity has been used to track DNA synthesis due to the high sensitivity that can be obtained using radioactive phosphorous labels11,18. Unfortunately, the high cost of disposal as well as the limited shelf life of radioactive labels can make the use of radioactive labels prohibitive. Here, we describe the use of near-infrared fluorophore labeled DNA, which does not suffer from these drawbacks. Notably, with near-infrared fluorescent dyes we see similar detection limits to radioactively labeled DNA (unpublished results). However, with fluorescent dyes in the visible range, we were not able to observe similar detection limits (unpublished results). While our group typically uses commercially prepared DNA bearing near-infrared fluorophores, these dyes are compatible with a number of established post-synthesis 5&#39; modification chemistries that can be used to install these labels.
Near-infrared fluorescent dyes are also advantageous in that there are multiple commercially available colors, which can enable more complex experiments that monitor synthesis of two labeled oligonucleotides in a single experiment. With radioactive labels, these types of multicomponent experiments are not easily executed. This will likely enable a number of more complex experiments, particularly for orthogonal replication experiments.
This assay, and any assay using denaturing polyacrylamide gel electrophoresis, is primarily limited by the technical challenge of executing the electrophoresis, the low throughput of these experiments, as well as the limited size ranges that are observable at single nucleotide resolution. We hope that this detailed protocol allows groups to overcome the technical challenges of these assays. Notably, while the throughput of the assay is limiting, the use of near-infrared fluorescent labels does increase the throughput, as it does not require the user to develop an autoradiograph. However, the gel still takes approximately 4-6 h to set up and run, limiting the number of experiments that can be run per day. The limited range is caused by the electrophoretic capabilities of polyacrylamide. Practically speaking, these limitations mean that these assays are best for focused research questions that require single nucleotide resolution.
Recently, high throughput DNA sequencing19 has been used increasingly as a method of characterizing DNA polymerases20,21. These assays are noteworthy for their dramatically increased throughput, which enables broader questions focused on sequence biases and error spectra. Importantly, while high throughput sequencing can enable many parallel experiments, it can be challenging to interpret on a single nucleotide basis. This provides an exciting opportunity for enzyme assays employing polyacrylamide gel electrophoresis to fill in the gaps in high throughput sequencing, ensuring that the methods described in this article are relevant for many years to come.

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>MgCl2</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&#8217;-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&#8217;-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 ladder or molecular marker is used. Occasionally, we will use a known polymerase-substrate combination to create a molecular marker; however, it is important to note that different modified nucleotides have very different electrophoretic mobilities, making comparison of oligonucleotides of the same length but differing nucleotide structure inappropriate.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56228/56228fig1.jpg" /> 
Figure 1: Example of successful polyacrylamide gel analysis of a qualitative characterization of overall activity. Note that the individual bands are well-defined and regular. The bands represent oligonucleotides of differing length; this gel enables easy comparison between polymerases. The no enzyme control lane is indicated with a &#34;-&#34;. Activity is judged by both the length of the products and the portion of the labeled primer that is converted to larger products. From this analysis, E6 and E5 are the most active. E3 and E2 are approximately equal in activity, but less than E6 or E5, and E4 and E1 are the least active enzymes.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56228/56228fig2.jpg" /> 
Figure 2: Example of successful gel for quantitative analysis using steady-state kinetics. Note that the bands are well resolved and well defined. To measure steady-state rate constants of individual steps in oligonucleotide synthesis, an enzyme is incubated with varying quantities of nucleoside triphosphate (in this case, dCTP); note that only the n and (n+1) products are synthesized enabling quantification of the singular event.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56228/56228fig3.jpg" /> 
Figure 3: Example of an unsuccessful gel for overall activity. The gel was torn during handling, resulting in visible gaps in bands. Note that the gel bands are irregularly shaped, making quantification and analysis difficult.

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

Nanyang Technological University

Research

JoVE Journal

Biochemistry

14.0K 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

Characterization of Multi-subunit Protein Complexes of Human MxA Using Non-denaturing Polyacrylamide Gel-electrophoresis

The formation of oligomeric complexes is a crucial prerequisite for the proper structure and function of many proteins. The interferon-induced antiviral effector protein MxA exerts a broad antiviral activity against many viruses. MxA is a dynamin-like GTPase and has the capacity to form oligomeric structures of higher order. However, whether oligomerization of MxA is required for its antiviral activity is an issue of debate. We describe here a simple protocol to assess the oligomeric state of endogenously or ectopically expressed MxA in the cytoplasmic fraction of human cell lines by non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with Western blot analysis. A critical step of the protocol is the choice of detergents to prevent aggregation and/or precipitation of proteins particularly associated with cellular membranes such as MxA, without interfering with its enzymatic activity. Another crucial aspect of the protocol is the irreversible protection of the free thiol groups of cysteine residues by iodoacetamide to prevent artificial interactions of the protein. This protocol is suitable for a simple assessment of the oligomeric state of MxA and furthermore allows a direct correlation of the antiviral activity of MxA interface mutants with their respective oligomeric states.

This article describes a simple and rapid protocol to evaluate the oligomeric state of the dynamin-like GTPase MxA protein from lysates of human cells using a combination of non-denaturing PAGE with western blot analysis.

The formation of oligomeric complexes is a crucial prerequisite for the proper structure and function of many proteins. The interferon-induced antiviral ...

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. ...

Real-time Tracking of DNA Fragment Separation by Smartphone

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and others. However, the traditional SGE protocol is quite tedious, and the experiment takes a long time. Moreover, the chemical consumption in SGE experiments is very high. This work proposes a simple method for the separation of DNA fragments based on an SGE chip. The chip is made by an engraving machine. Two plastic sheets are used for the excitation and emission wavelengths of the optical signal. The fluorescence signal of the DNA bands is collected by smartphone. To validate this method, 50, 100, and 1,000 bp DNA ladders were separated. The results demonstrate that a DNA ladder smaller than 5,000 bp can be resolved within 12 min and with high resolution when using this method, indicating that it is an ideal substitute for the traditional SGE method.

Traditional slab gel electrophoresis (SGE) experiments require a complicated apparatus and high chemical consumption. This work presents a protocol that describes a low-cost method to separate DNA fragments within a short timeframe.

Slab gel electrophoresis (SGE) is the most common method for the separation of DNA fragments; thus, it is broadly applied to the field of biology and ...

Horizontal Gel Electrophoresis for Enhanced Detection of Protein-RNA Complexes

Native polyacrylamide gel electrophoresis is a fundamental tool of molecular biology that has been used extensively for the biochemical analysis of RNA-protein interactions. These interactions have been traditionally analyzed with polyacrylamide gels generated between two glass plates and samples electrophoresed vertically. However, polyacrylamide gels cast in trays and electrophoresed horizontally offers several advantages. For example, horizontal gels used to analyze complexes between fluorescent RNA substrates and specific proteins can be imaged multiple times as electrophoresis progresses. This provides the unique opportunity to monitor RNA-protein complexes at several points during the experiment. In addition, horizontal gel electrophoresis makes it possible to analyze many samples in parallel. This can greatly facilitate time course experiments as well as analyzing multiple reactions simultaneously to compare different components and conditions. Here we provide a detailed protocol for generating and using horizontal native gel electrophoresis for analyzing RNA-Protein interactions.

Native polyacrylamide gel electrophoresis is a fundamental tool for analyzing RNA-protein interactions. Traditionally most experiments have used vertical gels. However, horizontal gels provide several advantages, such as the opportunity to monitor complexes during electrophoresis. We provide a detailed protocol for generating and using horizontal native gel electrophoresis.

Native polyacrylamide gel electrophoresis is a fundamental tool of molecular biology that has been used extensively for the biochemical analysis of ...

Analysis of AtHIRD11 Intrinsic Disorder and Binding Towards Metal Ions by Capillary Gel Electrophoresis and Affinity Capillary Electrophoresis

Plants are strongly dependent on their environment. In order to adjust to stressful changes (e.g., drought and high salinity), higher plants evolve classes of intrinsically disordered proteins (IDPs) to reduce oxidative and osmotic stress. This article uses a combination of capillary gel electrophoresis (CGE) and mobility shift affinity electrophoresis (ACE) in order to describe the binding behavior of different conformers of the IDP AtHIRD11 from Arabidopsis thaliana. CGE is used to confirm the purity of AtHIRD11 and to exclude fragments, posttranslational modifications, and other impurities as reasons for complex peak patterns. In this part of the experiment, the different sample components are separated by a viscous gel inside a capillary by their different masses and detected with a diode array detector. Afterward, the binding behavior of the sample towards various metal ions is investigated by ACE. In this case, the ligand is added to the buffer solution and the shift in migration time is measured in order to determine whether a binding event has occurred or not. One of the advantages of using the combination of CGE and ACE to determine the binding behavior of an IDP is the possibility to automate the gel electrophoresis and the binding assay. Furthermore, CGE shows a lower limit of detection than the classical gel electrophoresis and ACE is able to determine the manner of binding a ligand in a fast manner. In addition, ACE can also be applied to other charged species than metal ions. However, the use of this method for binding experiments is limited in its ability to determine the number of binding sites. Nevertheless, the combination of CGE and ACE can be adapted for characterizing the binding behavior of any protein sample towards numerous charged ligands.

This protocol combines the characterization of a protein sample by capillary gel electrophoresis and a fast-binding screening for charged ligands by affinity capillary electrophoresis. It is recommended for proteins with a flexible structure, such as intrinsically disordered proteins, to determine any differences in binding for different conformers.

Plants are strongly dependent on their environment. In order to adjust to stressful changes (e.g., drought and high salinity), higher plants evolve ...

Proofreading and DNA Repair Assay Using Single Nucleotide Extension and MALDI-TOF Mass Spectrometry Analysis

The maintenance of the genome and its faithful replication is paramount for conserving genetic information. To assess high fidelity replication, we have developed a simple non-labeled and non-radio-isotopic method using a matrix-assisted laser desorption ionization with time-of-flight (MALDI-TOF) mass spectrometry (MS) analysis for a proofreading study. Here, a DNA polymerase [e.g., the Klenow fragment (KF) of Escherichia coli DNA polymerase I (pol I) in this study] in the presence of all four dideoxyribonucleotide triphosphates is used to process a mismatched primer-template duplex. The mismatched primer is then proofread/extended and subjected to MALDI-TOF MS. The products are distinguished by the mass change of the primer down to single nucleotide variations. Importantly, a proofreading can also be determined for internal single mismatches, albeit at different efficiencies. Mismatches located at 2-4-nucleotides (nt) from the 3' end were efficiently proofread by pol I, and a mismatch at 5 nt from the primer terminus showed only a partial correction. No proofreading occurred for internal mismatches located at 6 - 9 nt from the primer 3' end. This method can also be applied to DNA repair assays (e.g., assessing a base-lesion repair of substrates for the endo V repair pathway). Primers containing 3' penultimate deoxyinosine (dI) lesions could be corrected by pol I. Indeed, penultimate T-I, G-I, and A-I substrates had their last 2 dI-containing nucleotides excised by pol I before adding a correct ddN 5'-monophosphate (ddNMP) while penultimate C-I mismatches were tolerated by pol I, allowing the primer to be extended without repair, demonstrating the sensitivity and resolution of the MS assay to measure DNA repair.

A non-labeled, non-radio-isotopic method for DNA polymerase proofreading and a DNA repair assay was developed by using high-resolution MALDI-TOF mass spectrometry and a single nucleotide extension strategy. The assay proved to be very specific, simple, rapid, and easy to perform for proofreading and repair patches shorter than 9-nucleotides.

The maintenance of the genome and its faithful replication is paramount for conserving genetic information. To assess high fidelity replication, we have ...

Analysis of Thylakoid Membrane Protein Complexes by Blue Native Gel Electrophoresis

Photosynthetic electron transfer chain (ETC) converts solar energy to chemical energy in the form of NADPH and ATP. Four large protein complexes embedded in the thylakoid membrane harvest solar energy to drive electrons from water to NADP+ via two photosystems, and use the created proton gradient for production of ATP. Photosystem PSII, PSI, cytochrome b6f (Cyt b6f) and ATPase are all multiprotein complexes with distinct orientation and dynamics in the thylakoid membrane. Valuable information about the composition and interactions of the protein complexes in the thylakoid membrane can be obtained by solubilizing the complexes from the membrane integrity by mild detergents followed by native gel electrophoretic separation of the complexes. Blue native polyacrylamide gel electrophoresis (BN-PAGE) is an analytical method used for the separation of protein complexes in their native and functional form. The method can be used for protein complex purification for more detailed structural analysis, but it also provides a tool to dissect the dynamic interactions between the protein complexes. The method was developed for the analysis of mitochondrial respiratory protein complexes, but has since been optimized and improved for the dissection of the thylakoid protein complexes. Here, we provide a detailed up-to-date protocol for analysis of labile photosynthetic protein complexes and their interactions in Arabidopsis thaliana.

A protocol for the elucidation of plant thylakoid protein complex organization and composition with blue native polyacrylamide gel electrophoresis (BN-PAGE) and 2D-SDS-PAGE is described. The protocol is optimized for Arabidopsis thaliana, but can be used for other plant species with minor modifications.

Photosynthetic electron transfer chain (ETC) converts solar energy to chemical energy in the form of NADPH and ATP. Four large protein complexes embedded ...

High Sensitivity Measurement of Transcription Factor-DNA Binding Affinities by Competitive Titration Using Fluorescence Microscopy

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing approaches suffer from significant limitations, we have developed a new method for determining TF-DNA binding affinities with high sensitivity on a large scale. The assay relies on the established fluorescence anisotropy (FA) principle but introduces important technical improvements. First, we measure a full FA competitive titration curve in a single well by incorporating TF and a fluorescently labeled reference DNA in a porous agarose gel matrix. Unlabeled DNA oligomer is loaded on the top as a competitor and, through diffusion, forms a spatio-temporal gradient. The resulting FA gradient is then read out using a customized epifluorescence microscope setup. This improved setup greatly increases the sensitivity of FA signal detection, allowing both weak and strong binding to be reliably quantified, even for molecules of similar molecular weights. In this fashion, we can measure one titration curve per well of a multi-well plate, and through a fitting procedure, we can extract both the absolute dissociation constant (KD) and active protein concentration. By testing all single-point mutation variants of a given consensus binding sequence, we can survey the entire binding specificity landscape of a TF, typically on a single plate. The resulting position weight matrices (PWMs) outperform those derived from other methods in predicting in vivo TF occupancy. Here, we present a detailed guide for implementing HiP-FA on a conventional automated fluorescent microscope and the data analysis pipeline.

Here we present a novel method for determining binding affinities at equilibrium and in solution with high sensitivity on a large scale. This improves the quantitative analysis of transcription factor-DNA binding. The method is based on automated fluorescence anisotropy measurements in a controlled delivery system.

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing ...

DNA Electrophoresis Using Thiazole Orange Instead of Ethidium Bromide or Alternative Dyes

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, DNA is visualized by staining. This article demonstrates how to use thiazole orange to stain DNA. Thiazole orange compares favorably to common staining methods, in that it is sensitive, inexpensive, excitable with UV or blue light (to prevent sample damage), and safer than ethidium bromide. Labs already equipped to run DNA electrophoresis experiments using ethidium bromide can generally switch dyes with no additional changes to existing protocols, using UV light for detection. Blue-light detection to avoid sample damage can additionally be achieved with a blue-light source and emission filter. Labs already equipped for blue-light detection can simply switch dyes with no additional changes to existing protocols.

Here, we present a protocol to use thiazole orange for the detection of DNA in gel electrophoresis experiments. The use of thiazole orange allows elimination of ethidium bromide, and fluorescence detection can be achieved with either UV or blue light.

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, ...

DNA Sequence Recognition by DNA Primase Using High-Throughput Primase Profiling

DNA primase synthesizes short RNA primers that initiate DNA synthesis of Okazaki fragments on the lagging strand by DNA polymerase during DNA replication. The binding of prokaryotic DnaG-like primases to DNA occurs at a specific trinucleotide recognition sequence. It is a pivotal step in the formation of Okazaki fragments. Conventional biochemical tools that are used to determine the DNA recognition sequence of DNA primase provide only limited information. Using a high-throughput microarray-based binding assay and consecutive biochemical analyses, it has been shown that 1) the specific binding context (flanking sequences of the recognition site) influences the binding strength of the DNA primase to its template DNA, and 2) stronger binding of primase to the DNA yields longer RNA primers, indicating higher processivity of the enzyme. This method combines PBM and primase activity assay and is designated as high-throughput primase profiling (HTPP), and it allows characterization of specific sequence recognition by DNA primase in unprecedented time and scalability.&#160;

Protein binding microarray (PBM) experiments combined with biochemical assays link the binding and catalytic properties of DNA primase, an enzyme that synthesizes RNA primers on template DNA. This method, designated as high-throughput primase profiling (HTPP), can be used to reveal DNA-binding patterns of a variety of enzymes.

DNA primase synthesizes short RNA primers that initiate DNA synthesis of Okazaki fragments on the lagging strand by DNA polymerase during DNA replication. ...