title: Saccharomyces cerevisiae Mer3 helicase stimulates 3'-5' heteroduplex extension by Rad51; implications for crossover control in meiotic recombination.
abstract: Crossover and noncrossover recombinants can form by two different pathways during meiotic recombination in Saccharomyces cerevisiae. The MER3 gene is known to affect selectively crossover, but not noncrossover, recombination. The Mer3 protein is a DNA helicase that unwinds duplex DNA in the 3' to 5' direction. To define the underlying molecular steps of meiotic recombination, we investigated the role of Mer3 helicase in DNA strand exchange promoted by Rad51 protein. We found that Mer3 helicase does not function as an initiator of DNA pairing events but, rather, it stimulates DNA heteroduplex extension in the 3' --> 5' direction relative to the incoming (or displaced) single-stranded DNA. Conversely, Mer3 helicase blocks DNA heteroduplex extension in the 5' --> 3' direction. Our results support the idea that Mer3 helicase stabilizes nascent joint molecules via DNA heteroduplex extension to permit capture of the second processed end of a double-stranded DNA break, a step which is required for crossover recombinant product formation.
authors.affiliation: Ludwig Institute for Cancer Research, Cancer Center and Department of Medicine, University of California San Diego School of Medicine, La Jolla, CA 92093, USA.
authors.forename: Olga M
authors.initials: OM
authors.lastname: Mazina
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Mazin
authors.forename: Takuro
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Richard D
authors.initials: RD
authors.lastname: Kolodner
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Kowalczykowski
mesh_terms: D004247:DNA / Q000235:genetics; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D045566:DNA, Cruciform / Q000235:genetics; D004277:DNA, Single-Stranded / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D008540:Meiosis / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics*; D051135:Rad51 Recombinase; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D045566:DNA, Cruciform; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D009692:Nucleic Acid Heteroduplexes; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA; C495151:RAD51 protein, S cerevisiae; D051135:Rad51 Recombinase; D011938:Rec A Recombinases; C455499:HFM1 protein, S cerevisiae; D004265:DNA Helicases