RecBCDKomplex

RecBCDKomplex, commonly referred to as the RecBCD complex, is a multi-subunit DNA helicase-nuclease enzyme found in many bacteria. It initiates repair of double-strand breaks by processing DNA ends and promoting homologous recombination, thereby contributing to genome stability and genetic diversity.

The complex is composed of three subunits: RecB, RecC, and RecD. RecB and RecD are motor proteins with helicase and nuclease activities, while RecC acts as a structural scaffold and contains the recognition site for the Chi sequence. The complex binds to a DNA end and unwinds the duplex, using ATP-driven translocation to separate and degrade DNA strands.

A key feature of RecBCDKomplex function is the Chi sequence, an 8-base pair DNA motif (for E. coli, 5'-GCTGGTGG-3' in the correct orientation) that modulates the nuclease activity of the complex. Upon encountering Chi, the complex undergoes a regulatory shift: degradation of the 3' end is reduced and RecA loading onto the resulting single-stranded DNA is promoted. This creates a 3' overhang onto which RecA can assemble, facilitating homology search and strand invasion required for homologous recombination.

Biological role and significance include repairing double-strand breaks, initiating recombination-based repair pathways, and influencing the SOS response under DNA-damaging conditions. The activity of RecBCDKomplex is essential for efficient end resection and proper recombination, contributing to genome integrity.

In bacteria, RecBCDKomplex-like activity is widespread, though some species rely on related end-resection systems such as AddAB. The RecBCD family remains a foundational model in studies of DNA repair, recombination mechanics, and the coordination of helicase, nuclease, and recombinase activities.