Complexes of RecA with LexA and RecX differentiate between active and inactive RecA nucleoprotein filaments

Margaret S. VanLoock, Xiong Yu, Shixin Yang, Vitold E. Galkin, Hao Huang, Shyamala S. Rajan, Wayne F. Anderson, Elizabeth A. Stohl, H. Steven Seifert, Edward H. Egelman*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations


The bacterial RecA protein has been the dominant model system for understanding homologous genetic recombination. Although a crystal structure of RecA was solved ten years ago, we still do not have a detailed understanding of how the helical filament formed by RecA on DNA catalyzes the recognition of homology and the exchange of strands between two DNA molecules. Recent structural and spectroscopic studies have suggested that subunits in the helical filament formed in the RecA crystal are rotated when compared to the active RecA-ATP-DNA filament. We examine RecA-DNA-ATP filaments complexed with LexA and RecX to shed more light on the active RecA filament. The LexA repressor and RecX, an inhibitor of RecA, both bind within the deep helical groove of the RecA filament. Residues on RecA that interact with LexA cannot be explained by the crystal filament, but can be properly positioned in an existing model for the active filament. We show that the strand exchange activity of RecA, which can be inhibited when RecX is present at very low stoichiometry, is due to RecX forming a block across the deep helical groove of the RecA filament, where strand exchange occurs. It has previously been shown that changes in the nucleotide bound to RecA are associated with large motions of RecA's C-terminal domain. Since RecX binds from the C-terminal domain of one subunit to the nucleotide-binding core of another subunit, a stabilization of RecA's C-terminal domain by RecX can likely explain the inhibition of RecA's ATPase activity by RecX.

Original languageEnglish (US)
Pages (from-to)345-354
Number of pages10
JournalJournal of Molecular Biology
Issue number2
StatePublished - Oct 17 2003


  • Electron microscopy
  • Helical polymers
  • Image analysis
  • Recombination

ASJC Scopus subject areas

  • Molecular Biology
  • Structural Biology


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