The recombination hot spot χ activates RecBCD recombination by converting Escherichia coli to a recD mutant phenocopy

Richard S. Myers, Andrei Kuzminov, Franklin W. Stahl

Research output: Contribution to journalArticle

49 Scopus citations


The products of the recB and recC genes are necessary for conjugal recombination and for repair of chromosomal double-chain breaks in Escherichia coli. The recD gene product combines with the RecB and RecC proteins to comprise RecBCD enzyme but is required for neither recombination nor repair. On the contrary, RecBCD enzyme is an exonuclease that inhibits recombination by destroying linear DNA. The RecD ejection model proposes that RecBCD enzyme enters a DNA duplex at a double-chain end and travels destructively until it encounters the recombination hot spot sequence χ · χ then alters the RecBCD enzyme by weakening the affinity of the RecD subunit for the RecBC heterodimer. With the loss of the RecD subunit, the resulting protein, RecBC(D-), becomes deficient for exonuclease activity and proficient as a recombinagenic helicase. To test the model, genetic crosses between A phage were conducted in cells containing χ on a nonhomologous plasmid. Upon delivering a double-chain break to the plasmid, λ recombined as if the cells had become recD mutants. The ability of χ to alter λ recombination in trans was reversed by overproducing the Reed subunit. These results indicate that χ can influence a recombination act without directly participating in it.

Original languageEnglish (US)
Pages (from-to)6244-6248
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number14
StatePublished - Jul 3 1995
Externally publishedYes



  • bacteriophage λ
  • exonuclease V
  • genetic recombination

ASJC Scopus subject areas

  • General

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