Promotion of Rad51-dependent D-loop formation by yeast recombination factor Rdh54/Tid1.

The first DNA joint formed in homologous recombination processes is a D-loop. Saccharomyces cerevisiae RDH54/TID1-encoded product, a Swi2/Snf2-like factor involved in recombination, is shown here to promote D-loop formation with Rad51 recombinase. Physical interaction between Rdh54 and Rad51 is functionally important because Rdh54 does not enhance the recombinase activity of the Escherichia coli RecA protein. Robust dsDNA-activated ATPase activity in Rdh54 generates unconstrained negative and positive supercoils in DNA. Efficient D-loop formation occurs with even topologically relaxed DNA, suggesting that via specific protein-protein interactions, the negative supercoils produced by Rdh54 are used by Rad51 for making DNA joints.