SS DNA-Binding Protein Is Dynamic and Critical to DNA Repair

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. In a series of experiments in E. coli, 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 single-stranded DNA 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," said Dr. Taekjip Ha, senior author of the study, which is reported in the October 22 issue of Nature. [Press release] [Nature News & Views] [Nature abstract]
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