A Domain of RecC Required for Assembly of the Regulatory RecD Subunit Into the Escherichia coli RecBCD Holoenzyme

Corresponding author: Gerald R. Smith, 1100 Fairview Ave. North, P.O. Box 19024, Seattle, WA 98109., gsmith{at}fhcrc.org (E-mail)

Communicating editor: L. S. SYMINGTON

The heterotrimeric RecBCD enzyme of Escherichia coli is required for the major pathway of double-strand DNA break repair and genetic exchange. Assembled as a heterotrimer, the enzyme has potent nuclease and helicase activity. Analysis of recC nonsense and deletion mutations revealed that the C terminus of RecC is required for assembly of the RecD subunit into RecBCD holoenzyme but not for recombination proficiency; the phenotype of these mutations mimics that of recD deletion mutations. Partial proteolysis of purified RecC polypeptide yielded a C-terminal fragment that corresponds to the RecD-interaction domain. RecD is essential for nuclease activity, regulation by the recombination hotspot Chi, and high affinity for DNA ends. The RecC-RecD interface thus appears critical for the regulation of RecBCD enzyme via the assembly and, we propose, disassembly or conformational change of the RecD subunit.

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