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 Researchers develop eco-friendly, 4-in-1 catalyst
25.04.2017 | Brown University

nachricht Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017
25.04.2017 | Laser Zentrum Hannover e.V.

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

NASA's Fermi catches gamma-ray flashes from tropical storms

25.04.2017 | Physics and Astronomy

Researchers invent process to make sustainable rubber, plastics

25.04.2017 | Materials Sciences

Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017

25.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>