The stretched DNA geometry of recombination and repair nucleoprotein filaments

Biopolymers. 2001-2002;61(3):145-58. doi: 10.1002/bip.10145.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.
  • Review

MeSH terms

  • Base Sequence
  • DNA Repair*
  • Escherichia coli / metabolism
  • Models, Biological
  • Molecular Sequence Data
  • Nucleoproteins / metabolism*
  • Protein Binding
  • Rec A Recombinases / genetics
  • Rec A Recombinases / metabolism
  • Recombination, Genetic*


  • Nucleoproteins
  • Rec A Recombinases