Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Single-stranded DNA-binding protein proven dynamic, critical to DNA repair

22.10.2009
Researchers report that a single-stranded DNA-binding protein (SSB), once thought to be a static player among the many molecules that interact with DNA, actually moves back and forth along single-stranded DNA, gradually allowing other proteins to repair, recombine or replicate the strands.

Their study, of SSB in the bacterium Escherichia coli, appears today in the journal Nature.

Whenever the double helix of DNA unravels, exposing each strand to the harsh environment of the cell, SSB is usually first on the scene, said University of Illinois physics professor and Howard Hughes Medical Institute investigator Taekjip Ha, who led the study.

Although DNA unwinding is necessary for replication or recombination, it is normally a transient process, he said. Exposed single-stranded DNA (ssDNA) can be damaged or degraded by enzymes in the cell. Damaged DNA may also come unwound, and ssDNA can bond to itself, forming hairpin loops and other problematic structures.

“If you have lots of single-stranded DNA in the cell, basically it’s a sign of trouble,” Ha said. “SSB needs to come and bind to it to protect it from degradation and to control what kind of proteins have access to the single-stranded DNA.”

Although other proteins are known to travel along double-stranded DNA, this is the first study to find a protein that migrates back and forth randomly on single-stranded DNA, Ha said.

Other researchers had assumed that SSB simply bound to DNA where it was needed and then fell off when its job was done. But a collaborator on the new study who has studied SSB for two decades, Timothy Lohman, of Washington University School of Medicine, suspected that the protein’s interaction with DNA was more dynamic. That hunch turned out to be true, Ha said.

The SSB protein is made up of four identical subunits. Single-stranded DNA loops around and through them in a pattern “that looks like the seam on a baseball,” Ha said. The DNA entry and exit points are very close to one another, making it possible to track the interaction of ssDNA and SSB using a technique called fluorescence resonance energy transfer (FRET).

FRET makes use of fluorescent molecules whose signals vary in intensity depending on their proximity to one another. By labeling different lengths of ssDNA with red and green dyes about 65 nucleotides apart (the length of ssDNA that threads through the SSB) and tracking the FRET signal as these single DNA molecules were exposed to SSB, the researchers were able to track the movement of SSB in relation to the single-stranded DNA.

In a series of experiments, the researchers showed that SSB diffuses randomly back and forth along single-stranded DNA, and that this movement is independent of the sequence of nucleotides that make up the DNA. They also found that an important DNA repair protein in E. coli, RecA, grows along the ssDNA in tandem with the movement of SSB. As the RecA protein extends along the DNA strand it prevents the backward movement of the SSB.

The researchers also found that SSB can “melt” small hairpin loops that appear in single-stranded DNA, straightening them so that the RecA protein can bind to and repair them. In this way SSB modulates the activity of RecA and other proteins that are involved in DNA repair, recombination and replication.

“SSB may be a master coordinator of all these important processes,” Ha said.

This research was supported by the National Science Foundation, the Howard Hughes Medical Institute and the National Institutes of Health. The study is a project of the NSF-funded Center for the Physics of Living Cells at the University of Illinois, which Ha co-directs with U. of I. physics professor Klaus Schulten. Ha also is an affiliate of the Institute for Genomic Biology.

Diana Yates | University of Illinois
Further information:
http://www.illinois.edu

More articles from Life Sciences:

nachricht New risk factors for anxiety disorders
24.02.2017 | Julius-Maximilians-Universität Würzburg

nachricht Stingless bees have their nests protected by soldiers
24.02.2017 | Johannes Gutenberg-Universität Mainz

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>