Name: direct observation of enzymes replicating dna using a single-molecule dna stretching assay
Uploaded: 2010-03-23T17:30:00
Description: Watch this Scientific Journal Video about Direct Observation of Enzymes Replicating DNA Using a Single-molecule DNA Stretching Assay at JoVE.com

The development of the DNA stretching assay was aided by Paul Blainey, Jong-Bong Lee, and Samir Hamdan. This work is supported by the National Institutes of Health grants to Charles Richardson (GM54397), and Antoine van Oijen (GM077248).

1. DNA Replication Template
DNA for the reaction is a linearized &lambda; DNA modified by annealing of oligonucleotides to form a replication fork. &nbsp;Additionally, biotin is attached to the end of one strand of the &lambda; DNA, and a digoxigenin moiety is attached to the other end of the same strand1.
Materials: Bacteriophage &lambda; DNA, Oligonucleotides: biotinylated fork arm (A: 5'-biotin-AAAAAAAAAAAAAAAAGAGTACTGTACGATCTAGCATCAA...

<ol>
	<li>Lee, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+primase+acts+as+a+molecular+brake+in+DNA+replication.">DNA primase acts as a molecular brake in DNA replication.</a> Nature. 439, 621-624 (2006).</li><li>Tanner, N. A., van Oijen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+observation+of+prokaryotic+DNA+replication.">Single-molecule observation of prokaryotic DNA replication.</a> Methods Mol Biol. 521, 397-410 (2009).</li><li>Sofia, S. J., Premnath, V. V., Merrill, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(ethylene+oxide)+Grafted+to+Silicon+Surfaces:+Grafting+Density+and+Protein+Adsorption.">Poly(ethylene oxide) Grafted to Silicon Surfaces: Grafting Density and Protein Adsorption.</a> Macromolecules. 31, 5059-5070 (1998).</li><li>Tanner, N. A., Loparo, J. J., van Oijen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+single-molecule+DNA+replication+with+fluorescence+microscopy.">Visualizing single-molecule DNA replication with fluorescence microscopy.</a> J Vis Exp. , (2009).</li><li>Hamdan, S. M., Loparo, J. J., Takahashi, M., Richardson, C. C., van Oijen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+DNA+replication+loops+reveal+temporal+control+of+lagging-strand+synthesis.">Dynamics of DNA replication loops reveal temporal control of lagging-strand synthesis.</a> Nature. 457, 336-339 (2009).</li><li>van Oijen, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+kinetics+of+lambda+exonuclease+reveal+base+dependence+and+dynamic+disorder.">Single-molecule kinetics of lambda exonuclease reveal base dependence and dynamic disorder.</a> Science. 301, 1235-1238 (2003).</li></ol>

It is important to ensure that the drag force exerted on beads by laminar flow doesn't influence enzymatic activities of the replication proteins. For instance, a 3 pN force that corresponds to a flow rate of 0.012 ml/min does not affect replication of the DNA leading strand. It does however affect enzymatic activities that take place during coordinated DNA synthesis, and it therefore has to be reduced to 1.5 pN. The drag force can be easily controlled by changing the flow rate or a width of the flow channel5....

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		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>Bacteriophage &lambda; DNA</td>
<td>&nbsp;</td>
<td>New England Biolabs</td>
<td>N3011L</td>
<td>&nbsp;</td>
<tr>
<td>DNA Oligonucleotides</td>
<td>&nbsp;</td>
<td>Integrated DNA Technologies</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>T4 DNA Ligase</td>
<td>&nbsp;</td>
<td>New England Biolabs</td>
<td>M0202L</td>
<td>&nbsp;</td>
<tr>
<td>T4 Polynucleotide Kinase</td>
<td>&nbsp;</td>
<td>New England Biolabs</td>
<td>M0201L</td>
<td>&nbsp;</td>
<tr>
<td>&alpha;-digoxigenin Fab</td>
<td>&nbsp;</td>
<td>Roche</td>
<td>11214667001</td>
<td>&nbsp;</td>
<tr>
<td>Tosyl Activated Beads</td>
<td>&nbsp;</td>
<td>Dynal/Invitrogen</td>
<td>142-03</td>
<td>&nbsp;</td>
<tr>
<td>Magnetic Separator</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>Dynal MPC</td>
<td>&nbsp;</td>
<tr>
<td>3-aminopropyl-triethoxysilane</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>A3648</td>
<td>Other aminosilanes can be used or mixed with non-amine reactive silanes for sparser surfaces</td>
</tr>
<tr>
<td>Succinimidyl propionate PEG</td>
<td>&nbsp;</td>
<td>Nektar</td>
<td>&nbsp;</td>
<td>Similar PEGs can be purchased from Nanocs, CreativePEGWorks, etc.</td>
</tr>
<tr>
<td>Biotin-PEG-NHS</td>
<td>&nbsp;</td>
<td>Nektar</td>
<td>&nbsp;</td>
<td>Similar PEGs can be purchased from Nanocs, CreativePEGWorks, etc.</td>
</tr>
<tr>
<td>Double-sided tape</td>
<td>&nbsp;</td>
<td>Grace BioLabs</td>
<td>SA-S-1L</td>
<td>100 &mu;m thickness</td>
</tr>
<tr>
<td>Quartz slide</td>
<td>&nbsp;</td>
<td>Technical Glass</td>
<td>20 mm (W)x 50 mm (L)x 1mm (H)</td>
<td>Size to fit on coverslips. Drill holes with diamond-tip drill bits (DiamondBurs.net)</td>
</tr>
<tr>
<td>Polyethylene tubing</td>
<td>&nbsp;</td>
<td>Becton Dickinson</td>
<td>427416</td>
<td>0.76 mm ID, 1.22 OD 
Other size tubing can be substituted.</td>
</tr>
<tr>
<td>Streptavidin</td>
<td>&nbsp;</td>
<td>Sigma</td>
<td>S4762</td>
<td>Make 1 mg/mL solution, 25 &mu;L aliquots in PBS pH 7.3</td>
</tr>
<tr>
<td>Deoxyribonucleotide triphosphate solution mix</td>
<td>&nbsp;</td>
<td>New England Biolabs</td>
<td>N0447</td>
<td>&nbsp;</td>
<tr>
<td>Inverted Optical Microscope with 10X Objective</td>
<td>&nbsp;</td>
<td>Olympus</td>
<td>Olympus IX-51</td>
<td>&nbsp;</td>
<tr>
<td>Permament rare-earth magnet</td>
<td>&nbsp;</td>
<td>National Imports</td>
<td>www.rare-earth-magnets.com</td>
<td>&nbsp;</td>
<tr>
<td>CCD Camera</td>
<td>&nbsp;</td>
<td>QImaging</td>
<td>Rolera-XR Fast 139</td>
<td>&nbsp;</td>
<tr>
<td>Syringe Pump</td>
<td>&nbsp;</td>
<td>Harvard Apparatus</td>
<td>11 Plus</td>
<td>Operate in refill mode to facilitate solution changes</td>
</tr>
<tr>
<td>Fiber Illuminator</td>
<td>&nbsp;</td>
<td>Thorlabs Inc.</td>
<td>OSL1</td>
<td>&nbsp;</td>		</tbody>
		</table>
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direct observation of enzymes replicating dna using a single-molecule dna stretching assay

We describe a method for observing real time replication of individual DNA molecules mediated by proteins of the bacteriophage replication system. Linearized &lambda; DNA is modified to have a biotin on the end of one strand, and a digoxigenin moiety on the other end of the same strand. The biotinylated end is attached to a functionalized glass coverslip and the digoxigeninated end to a small bead. The assembly of these DNA-bead tethers on the surface of a flow cell allows a laminar flow to be applied to exert a drag force on the bead. As a result, the DNA is stretched close to and parallel to the surface of the coverslip at a force that is determined by the flow rate (Figure 1). The length of the DNA is measured by monitoring the position of the bead. Length differences between single- and double-stranded DNA are utilized to obtain real-time information on the activity of the replication proteins at the fork. Measuring the position of the bead allows precise determination of the rates and processivities of DNA unwinding and polymerization (Figure 2).

Watch this Scientific Journal Video about Direct Observation of Enzymes Replicating DNA Using a Single-molecule DNA Stretching Assay at JoVE.com

Direct Observation of Enzymes Replicating DNA Using a Single-molecule DNA Stretching Assay

We describe a method for observing real time replication of individual DNA molecules mediated by proteins of the bacteriophage replication system.

We describe a method for observing real time replication of individual DNA molecules mediated by proteins of the bacteriophage replication system. ...

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