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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.
