title: ATPase and DNA helicase activities of the Saccharomyces cerevisiae anti-recombinase Srs2.
abstract: Saccharomyces cerevisiae SRS2 encodes an ATP-dependent DNA helicase that is needed for DNA damage checkpoint responses and that modulates the efficiency of homologous recombination. Interestingly, strains simultaneously mutated for SRS2 and a variety of DNA repair genes show low viability that can be overcome by inactivating homologous recombination, thus implicating inappropriate recombination as the cause of growth impairment in these mutants. Here, we report on our biochemical characterization of the ATPase and DNA helicase activities of Srs2. ATP hydrolysis by Srs2 occurs efficiently only in the presence of DNA, with ssDNA being considerably more effective than dsDNA in this regard. Using homopolymeric substrates, the minimal DNA length for activating ATP hydrolysis is found to be 5 nucleotides, but a length of 10 nucleotides is needed for maximal activation. In its helicase action, Srs2 prefers substrates with a 3' ss overhang, and approximately 10 bases of 3' overhanging DNA is needed for efficient targeting of Srs2 to the substrate. Even though a 3' overhang serves to target Srs2, under optimized conditions blunt-end DNA substrates are also dissociated by this protein. The ability of Srs2 to unwind helicase substrates with a long duplex region is enhanced by the inclusion of the single-strand DNA-binding factor replication protein A.
authors.affiliation: Institute of Biotechnology and Department of Molecular Medicine, University of Texas Health Science Center, San Antonio, Texas 78245, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Van Komen
authors.forename: Mothe Sreedhar
authors.initials: MS
authors.lastname: Reddy
authors.forename: Lumir
authors.initials: L
authors.lastname: Krejci
authors.forename: Hannah
authors.initials: H
authors.lastname: Klein
authors.forename: Patrick
authors.initials: P
authors.lastname: Sung
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D004247:DNA / Q000378:metabolism / Q000494:pharmacology; D004265:DNA Helicases / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D004277:DNA, Single-Stranded; D029701:Saccharomyces cerevisiae Proteins; C061376:SRS2 protein, S cerevisiae; D008345:Manganese; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D008274:Magnesium