THE HUMAN RAD54 RECOMBINATIONAL DNA-REPAIR PROTEIN IS A DOUBLE-STRANDED DNA-DEPENDENT ATPASE

DNA double-strand break repair through the RAD52 homologous recombinat ion pathway in the yeast Saccharomyces cerevisiae requires, among othe rs, the RAD51, RAD52, and RAD54 genes. The biological importance of ho mologous recombination is underscored by the conservation of the RAD52 pathway from fungi to humans. The critical roles of the RAD52 group p roteins in the early steps of recombination, the search for DNA homolo gy and strand exchange, are now becoming apparent. Here, we report the purification of the human Rad54 protein. We showed that human Rad54 h as ATPase activity that is absolutely dependent on double-stranded DNA . Unexpectedly, the ATPase activity appeared not absolutely required f or the DNA repair function of human Rad54 in vivo. Despite the presenc e of amino acid sequence motifs that are conserved in a large family o f DNA helicases, no helicase activity of human Rad54 was observed on a variety of different DNA substrates. Possible functions of human Rad5 4 in homologous recombination that couple the energy gained from ATP h ydrolysis to translocation along DNA, rather than disruption of base p airing, are discussed.