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Dec 14, 2012

For DNA, the Fix Is In

  • A newly-published paper offers insight into a mystery long associated with DNA repair—namely, how a protein involved in the process matches up a broken strand with an intact region of double-stranded DNA.

    While it was known that the repair protein RecA in bacterial cells guides broken DNA strands to a matching sequence on an adjoining bit of double-stranded DNA, scientists have not known until lately just how that protein did its job.

    “Because the genomic DNA is millions of bases long, this task is much like finding a needle in a haystack. We found the answer to how the cell does this so quickly,” Taekjip Ha, Ph.D., who led the study, said in a statement. Dr. Ha is a physics professor at University of Illinois, where he is also co-director of its NSF Center for the Physics of Living Cells.

    Dr. Ha’s research team used fluorescence resonance energy transfer (FRET) to observe in real time the interaction of the RecA protein and the DNA. Researchers labeled a single DNA strand bound by RecA, then placed a different fluorescent label on a stretch of double-stranded DNA, to see how the molecules interacted with one another.

    The result: The RecA that was bound to a broken, single-stranded DNA molecule slid back and forth along the double-stranded DNA molecule, searching for a match.

    “We discovered that this RecA filament can slide on double-stranded DNA for a span of sequences covering about 200 base pairs of DNA,” Dr. Ha said. “We did a calculation that found that, without this kind of process that we discovered, then DNA repair would be 200 times slower.”

    The functioning of RecA in DNA repair is detailed in a paper published in eLife, a new open-access journal supported by the Max Planck Society, the Wellcome Trust, and the Howard Hughes Medical Institute (HHMI), where Dr. Ha is also an investigator.

    The paper is available here.


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