The RecA binding locus of RecBCD is a general domain for recruitment of DNA strand exchange proteins

RecBCD enzyme facilitates loading of RecA protein onto ssDNA produced by its helicase/nuclease activity. This process is essential for RecBCD-mediated homologous recombination. Here, we establish that the C-terminal nuclease domain of the RecB subunit (RecB(nuc)) forms stable complexes with RecA. Interestingly, RecBnuc also interacts with and loads noncognate DNA strand exchange proteins. Interaction is with a conserved element of the RecA-fold, but because the binding to noncognate proteins decreases in a phylogenetically consistent way, species-specific interactions are also present. RecB(nuc) does not impede activities of RecA that are important to DNA strand exchange, consistent with its role in targeting of RecA. Modeling predicts the interaction interface for the RecA-RecBCD complex. Because a similar interface is involved in the binding of human Rad51 to the conserved BRC repeat of BRCA2 protein, the RecB-domain may be one of several structural domains that interact with and recruit DNA strand exchange proteins to DNA.