Featured Research

from universities, journals, and other organizations

Crucial step in human DNA replication observed for the first time

Date:
April 1, 2013
Source:
Penn State
Summary:
An elusive step in the process of human DNA replication has been observed, for the first time, by scientists. The step, which is crucial for DNA replication in humans and other forms of life, had previously remained mysterious and had not been well studied in human DNA.

Stephen J. Benkovic, Mark Hedglin, and other members of Professor Benkovic's research team have studied the importance of "clamp loader" enzymes and their activities during DNA replication. In this image, the clamp loader is represented, for illustrative purposes, by a hand, which is loading the sliding clamp ring onto DNA.
Credit: Benkovic lab, Penn State University

For the first time, an elusive step in the process of human DNA replication has been demystified by scientists at Penn State University. According to senior author Stephen J. Benkovic, an Evan Pugh Professor of Chemistry and Holder of the Eberly Family Chair in Chemistry at Penn State, the scientists "discovered how a key step in human DNA replication is performed."

Related Articles


The results of the research will be published in the journal eLife on 2 April 2013.

Part of the DNA replication process -- in humans and in other life forms -- involves loading of molecular structures called sliding clamps onto DNA. This crucial step in DNA replication had remained somewhat mysterious and had not been well studied in human DNA replication. Mark Hedglin, a post-doctoral researcher in Penn State's Department of Chemistry and a member of Benkovic's team, explained that the sliding clamp is a ring-shaped protein that acts to encircle the DNA strand, latching around it like a watch band. The sliding clamp then serves to anchor special enzymes called polymerases to the DNA, ensuring efficient copying of the genetic material. "Without a sliding clamp, polymerases can copy very few bases -- the molecular 'letters' that make up the code of DNA -- at a time. But the clamp helps the polymerase to stay in place, allowing it to copy thousands of bases before being removed from the strand of DNA," Hedglin said.

Hedglin explained that, due to the closed circular structure of sliding clamps, another necessary step in DNA replication is the presence of a "clamp loader," which acts to latch and unlatch the sliding clamps at key stages during the process. "The big unknown has always been how the sliding clamp and the clamp loader interact and the timing of latching and unlatching of the clamp from the DNA," said Hedglin. "We know that polymerases and clamp loaders can't bind the sliding clamp at the same time, so the hypothesis was that clamp loaders latched sliding clamps onto DNA, then left for some time during DNA replication, returning only to unlatch the clamps after the polymerase left so they could be recycled for further use."

To test this hypothesis, the team of researchers used a method called Fφrster resonance energy transfer (FRET), a technique of attaching fluorescent "tags" to human proteins and sections of DNA in order to monitor the interactions between them. "With these tags in place, we then observed the formation of holoenzymes -- the active form of the polymerase involved in DNA replication, which consists of the polymerase itself along with any accessory factors that optimize its activity," Hedglin said. "We found that whenever a sliding clamp is loaded onto a DNA template in the absence of polymerase, the clamp loader quickly removed the clamp so that free clamps did not build up on the DNA. However, whenever a polymerase was present, it captured the sliding clamp and the clamp loader then dissociated from the DNA strand."

The team members also found that, during the moments when both the clamp loader and the clamp were bound to the DNA, they were not intimately engaged with each other. Rather, the clamp loader released the closed clamp onto the DNA, allowing an opportunity for the polymerase to capture the clamp, completing the assembly of the holoenzyme. Subsequently, the clamp loader dissociated from DNA. "Our research demonstrates that the DNA polymerase holoenzyme in humans consists of only a clamp and a DNA polymerase. The clamp loader is not part of it. It disengages from the DNA after the polymerase binds the clamp," Hedglin added.

Benkovic noted that this mechanism provides a means for the cell to recycle scarce clamps when they are not in use for productive replication.

In addition to Benkovic and Hedglin, other Penn State researchers who contributed to the paper include Senthil K Perumal and Zhenxin Hu.

The research was funded by the National Institutes of Health.


Story Source:

The above story is based on materials provided by Penn State. Note: Materials may be edited for content and length.


Journal Reference:

  1. Mark Hedglin, Senthil K Perumal, Zhenxin Hu, Stephen Benkovic. Stepwise assembly of the human replicative polymerase holoenzyme. eLife, 2013; (in press) [link]

Cite This Page:

Penn State. "Crucial step in human DNA replication observed for the first time." ScienceDaily. ScienceDaily, 1 April 2013. <www.sciencedaily.com/releases/2013/04/130401151039.htm>.
Penn State. (2013, April 1). Crucial step in human DNA replication observed for the first time. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2013/04/130401151039.htm
Penn State. "Crucial step in human DNA replication observed for the first time." ScienceDaily. www.sciencedaily.com/releases/2013/04/130401151039.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Pet Dogs to Be Used in Anti-Ageing Trial

Pet Dogs to Be Used in Anti-Ageing Trial

Reuters - Innovations Video Online (Nov. 26, 2014) — Researchers in the United States are preparing to discover whether a drug commonly used in human organ transplants can extend the lifespan and health quality of pet dogs. Video provided by Reuters
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) — Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. Video provided by Newsy
Powered by NewsLook.com
From Popcorn To Vending Snacks: FDA Ups Calorie Count Rules

From Popcorn To Vending Snacks: FDA Ups Calorie Count Rules

Newsy (Nov. 25, 2014) — The US FDA is announcing new calorie rules on Tuesday that will require everywhere from theaters to vending machines to include calorie counts. Video provided by Newsy
Powered by NewsLook.com
Daily Serving Of Yogurt Could Reduce Risk Of Type 2 Diabetes

Daily Serving Of Yogurt Could Reduce Risk Of Type 2 Diabetes

Newsy (Nov. 25, 2014) — Need another reason to eat yogurt every day? Researchers now say it could reduce a person's risk of developing type 2 diabetes. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins