title: The poor homology stringency in the heteroduplex allows strand exchange to incorporate desirable mismatches without sacrificing recognition in vivo.
abstract: RecA family proteins are responsible for homology search and strand exchange. In bacteria, homology search begins after RecA binds an initiating single-stranded DNA (ssDNA) in the primary DNA-binding site, forming the presynaptic filament. Once the filament is formed, it interrogates double-stranded DNA (dsDNA). During the interrogation, bases in the dsDNA attempt to form Watson-Crick bonds with the corresponding bases in the initiating strand. Mismatch dependent instability in the base pairing in the heteroduplex strand exchange product could provide stringent recognition; however, we present experimental and theoretical results suggesting that the heteroduplex stability is insensitive to mismatches. We also present data suggesting that an initial homology test of 8 contiguous bases rejects most interactions containing more than 1/8 mismatches without forming a detectable 20 bp product. We propose that, in vivo, the sparsity of accidental sequence matches allows an initial 8 bp test to rapidly reject almost all non-homologous sequences. We speculate that once the initial test is passed, the mismatch insensitive binding in the heteroduplex allows short mismatched regions to be incorporated in otherwise homologous strand exchange products even though sequences with less homology are eventually rejected.
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Claudia
authors.initials: C
authors.lastname: Danilowicz
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Darren
authors.initials: D
authors.lastname: Yang
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Craig
authors.initials: C
authors.lastname: Kelley
authors.affiliation: Laboratoire de Biochimie Théorique, CNRS UPR 9080, Univ. Paris Diderot, Sorbonne Paris Cité, IBPC, Paris, France.
authors.forename: Chantal
authors.initials: C
authors.lastname: Prévost
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138, USA prentiss@fas.harvard.edu.
authors.forename: Mara
authors.initials: M
authors.lastname: Prentiss
mesh_terms: D020137:Base Pair Mismatch; D059371:DNA, B-Form / Q000737:chemistry / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011938:Rec A Recombinases / Q000737:chemistry / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D059371:DNA, B-Form; D004277:DNA, Single-Stranded; D009692:Nucleic Acid Heteroduplexes; D011938:Rec A Recombinases