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 Topologische Quantenchemie
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

nachricht Topological Quantum Chemistry
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>