Direct visualization of RecBCD movement reveals cotranslocation of the RecD motor after χ recognition

Naofumi Handa, Piero R. Bianco, Ronald J. Baskin, Stephen C. Kowalczykowski

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In Escherichia coli, χ (5′-GCTGGTGG-3′) is a recombination hotspot recognized by the RecBCD enzyme. Recognition of χ reduces both nuclease activity and translocation speed of RecBCD and activates RecA-loading ability. RecBCD has two motor subunits, RecB and RecD, which act simultaneously but independently. A longstanding hypothesis to explain the changes elicited by χ interaction has been "ejection" of the RecD motor from the holoenzyme at χ. To test this proposal, we visualized individual RecBCD molecules labeled via RecD with a fluorescent nanoparticle. We could directly see these labeled, single molecules of RecBCD moving at up to 1835 bp/s (∼0.6 μm/s). Those enzymes translocated to χ, paused, and continued at reduced velocity, without loss of RecD. We conclude that χ interaction induces a conformational change, resulting from binding of χ to RecC, and not from RecD ejection. This change is responsible for alteration of RecBCD function that persists for the duration of DNA translocation.

Original languageEnglish (US)
Pages (from-to)745-750
Number of pages6
JournalMolecular Cell
Issue number5
StatePublished - Mar 4 2005


ASJC Scopus subject areas

  • Molecular Biology

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