Saccharomyces cerevisiae RDH54 is a key member of the evolutionarily conserved RAD52 epistasis group of genes needed for homologous recombination and DNA double strand break repair. The RDH54-encoded protein possesses a DNA translocase activity and functions together with the Rad51 recombinase in the D-loop reaction. By chromatin immunoprecipitation (ChIP), we show that Rdh54 is recruited, in a manner that is dependent on Rad51 and Rad52, to a site-specific DNA double strand break induced by the HO endonuclease. Because of its relatedness to Swi2/Snf2 chromatin remodelers, we have asked whether highly purified Rdh54 possesses chromatin-remodeling activity. Importantly, our results show that Rdh54 can mobilize a mononucleosome along DNA and render nucleosomal DNA accessible to a restriction enzyme, indicative of a chromatin-remodeling function. Moreover, Rdh54 co-operates with Rad51 in the utilization of naked or chromatinized DNA as template for D-loop formation. We also provide evidence for a strict dependence of the chromatin-remodeling attributes of Rdh54 on its ATPase activity and N-terminal domain. Interestingly, an N-terminal deletion mutant (rdh54⌬102) is unable to promote Rad51-mediated D-loop formation with a chromatinized template, while retaining substantial activity with naked DNA. These features of Rdh54 suggest a role of this protein factor in chromatin rearrangement during DNA recombination and repair.The genomic DNA in eukaryotic cells is organized into chromatin, which harbors repeated nucleosome units each comprising an octamer of four histone proteins, H2A, H2B, H3, and H4, and 147 bp of DNA (1, 2). The folding of DNA on the surface of histone proteins within the nucleosome inevitably poses an accessibility problem during various DNA transactions, including DNA replication, recombination, and repair.One mechanism to efficiently overcome this structural hindrance is by an ATP hydrolysis-dependent chromatin-remodeling process, such that remodeling proteins render DNA more accessible by weakening DNA:histone contacts, sliding nucleosomes along DNA, or removing H2A-H2B dimers from the nucleosome (3-5).We are interested in delineating the mechanism of homologous recombination (HR) 2 that is mediated by proteins of the RAD52 epistasis group, including how the HR machinery negotiates the constraints posed by chromatin structure. Regarding the latter, of special interest are two key members of the RAD52 epistasis group, Rad54 and Rdh54 proteins. These HR factors play multifaceted roles in HR (6 -8), and they belong to the Swi2/Snf2 protein superfamily, members of which are well known ATP hydrolysis-dependent chromatin remodelers (9, 10). Rad54 and Rdh54 both possess a DNA-dependent ATPase activity and a dsDNA translocase function that is fueled by ATP hydrolysis (8,(11)(12)(13)(14)(15). The DNA translocase activity of these Swi2/Snf2-like HR factors can modify DNA topology (11-13), enhance D-loop formation by the Rad51 recombinase (11, 16), accelerate the rate at which DNA strands are exchanged duri...