title: The stretched DNA geometry of recombination and repair nucleoprotein filaments.
abstract: The RecA protein of Escherichia coli plays essential roles in homologous recombination and restarting stalled DNA replication forks. In vitro, the protein mediates DNA strand exchange between single-stranded (ssDNA) and homologous double-stranded DNA (dsDNA) molecules that serves as a model system for the in vivo processes. To date, no high-resolution structure of the key intermediate, comprised of three DNA strands simultaneously bound to a RecA filament (RecA x tsDNA complex), has been elucidated by classical methods. Here we review the systematic characterization of the helical geometries of the three DNA strands of the RecA x tsDNA complex using fluorescence resonance energy transfer (FRET) under physiologically relevant solution conditions. Measurements of the helical parameters for the RecA x tsDNA complex are consistent with the hypothesis that this complex is a late, poststrand-exchange intermediate with the outgoing strand shifted by about three base pairs with respect to its registry with the incoming and complementary strands. All three strands in the RecA x tsDNA complex adopt extended and unwound conformations similar to those of RecA-bound ssDNA and dsDNA.
authors: Department of Chemistry, Rice University, P. O. Box 1892, MS 65, Houston, TX 77005, USA. sfs@rice.edu
authors: S F
authors: SF
authors: Singleton
authors: J
authors: J
authors: Xiao
mesh_terms: D001483:Base Sequence; D004260:DNA Repair; D004926:Escherichia coli / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009698:Nucleoproteins / Q000378:metabolism*; D011485:Protein Binding; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic
chemical_list: D009698:Nucleoproteins; D011938:Rec A Recombinases