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SSB, a dynamic protector of single-stranded DNA

Researchers report that a single-stranded DNA-binding protein (SSB) in the bacterium E. coli, 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.

Whenever the double helix of DNA unravels, exposing each strand to the harsh environment of the cell, SSB is usually first on the scene. Although DNA unwinding is necessary for replication or recombination, it is normally a transient process. 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," said Taekjip Ha who led the study. "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.

Source :
DNA-binding Protein Is Dynamic, Critical To DNA Repair. /ScienceDaily/. Retrieved November 2, 2009, on http://www.sciencedaily.com­ /releases/2009/10/091021115018.htm


The work has been published in Nature:
SSB protein diffusion on single-stranded DNA stimulates RecA filament formation.
Roy R, Kozlov AG, Lohman TM, Ha T
Nature. 2009 Oct 22;461(7267):1092-7. Epub 2009 Oct 11.

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