RecD

RecD is a gene encoding the RecD subunit of the bacterial RecBCD enzyme complex, a key player in the repair of double-strand breaks (DSBs) and in homologous recombination. The RecD protein functions as a DNA helicase and nuclease component that associates with RecB and RecC to process DNA ends before recombination.

In organisms such as Escherichia coli, the RecBCD complex binds to a DSB, unwinds the DNA, and degrades the ends to generate a 3' single-stranded overhang. RecD contributes to the complex’s 5' to 3' exonuclease activity and the overall nuclease action. As the complex translocates, it encounters Chi sites (a defined DNA sequence motif in the host genome). Encounter with Chi modulates nuclease activity and promotes loading of RecA onto the 3' overhang, initiating strand invasion and homologous recombination. The presence of RecD influences the balance between degradation and recombination and helps regulate the efficiency of repair.

Genetically, recD is typically located in the recBCD operon with recB and recC in many Gram-negative bacteria. However, some species lack RecD or replace the RecBCD pathway with alternative systems such as AddAB, reflecting diversity in DSB repair strategies across bacteria.

RecD is of interest in molecular genetics for understanding the mechanics of DSB processing and recombination. Mutations in recD alter nuclease activity, DNA damage sensitivity, and recombination phenotypes. The RecBCD/RecD system remains a foundational model for studying bacterial DNA repair and homologous recombination, and variations across species illustrate the evolutionary diversity of these pathways.