The DNA binding properties of Saccharomyces cerevisiae Rad51 protein

Saccharomyces cerevisiae Rad51 protein is the para-digm for eukaryotic ATP-dependent DNA strand ex-change proteins. To explain some of the unique charac-teristics of DNA strand exchange promoted by Rad51 protein, when compared with its prokaryotic homo-logue the Escherichia coli RecA protein, we analyzed the DNA binding properties of the Rad51 protein. Rad51 protein binds both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in an ATP- and Mg21-de-pendent manner, over a wide range of pH, with an ap-parent binding stoichiometry of approximately 1 pro-tein monomer per 4 (61) nucleotides or base pairs, respectively. Only dATP and adenosine 5*-g-(thiotri-phosphate) (ATPgS) can substitute for ATP, but binding in the presence of ATPgS requires more than a 5-fol