THE PREFERENCE FOR GT-RICH DNA BY THE YEAST RAD51 PROTEIN DEFINES A SET OF UNIVERSAL PAIRING SEQUENCES

The Rad51 protein of Saccharomyces cerevisiae is a eukaryotic homolog of the RecA protein, the prototypic DNA strand-exchange protein of Esc herichia coli. RAD51 gene function is required for efficient genetic r ecombination and for DNA double-strand break repair. Recently, we demo nstrated that RecA protein has a preferential affinity for GT-rich DNA sequences-several of which exhibit enhanced RecA protein-promoted hom ologous pairing activity. The fundamental similarity between the RecA and Rad51 proteins suggests that Rad51 might display an analogous bias . Using in vitro selection, here we show that the yeast Rad51 protein shares the same preference for GT-rich sequences as its prokaryotic co unterpart. This bias is also manifest as an increased ability of Rad51 protein to promote the invasion of supercoiled DNA by homologous GT-r ich single-stranded DNA, an activity not previously described for the eukaryotic pairing protein. We propose that the preferred utilization of GT-rich sequences is a conserved feature among all homologs of RecA protein, and that GT-rich regions are loci for increased genetic exch ange in both prokaryotes and eukaryotes.