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Recombinase Enzymes Recognize Matching DNA Three Bases at a Time

Patrick Sung, D.Phil.
Yale University
NIEHS Grant R01ES015252

The exchange of genetic information between DNA strands, known as DNA recombination, is important for DNA repair and also drives evolution. New research, funded in part by NIEHS, has revealed the physical basis for these DNA strand exchange reactions.

The study authors previously developed single-molecule methods to visualize DNA recombination using an imaging technique known as total internal reflection fluorescence microscopy. Using this imaging approach and molecular dynamics simulation they showed that members of the Rad51/RecA family of recombinase enzymes, which are responsible for DNA recombination, search for and recognize matching DNA strands three bases at a time.

The researchers studied four different recombinases: Escherichia coli RecA, human Rad51, eukaryotic forms of RecA, or Saccharomyces cerevisiae Dmc1. Dmc1 is specialized for meiotic recombination. The imaging studies showed that bacterial RecA and eukaryotic Rad51 and Dmc1 all stabilize strand exchange intermediates in precise three-nucleotide steps, a finding that was confirmed using molecular dynamics simulation. Additionally, the researchers found that while Rad51, RecA, and Dmc1 can all step over DNA mismatches, only Dmc1 can stabilize a mismatching triplet. This discovery provides insight into why eukaryotes evolved a recombinase that is specialized for meiosis.

Citation: Lee JY, Terakawa T, Qi Z, Steinfeld JB, Redding S, Kwon Y, Gaines WA, Zhao W, Sung P, Greene EC. 2015. Base triplet stepping by the Rad51/RecA family of recombinases. Science 349(6251):977-981.