Reciprocal control of catalysis by the tyrosine recombinases XerC and XerD: An enzymatic switch in site-specific recombination

In Xer site-specific recombination, sequential DNA strand exchange reaction s are catalyzed by a heterotetrameric complex composed of two recombinases, XerC and XerD. It is demonstrated that XerC and XerD catalytic activity is controlled by an interaction involving the C-terminal end of each protein (the donor region) and an internal region close to the active site (the acc eptor region). Mutations in these regions reciprocally alter the relative a ctivity of XerC and XerD, with their combination producing synergistic effe cts on catalysis. The data support a model in which C-terminal intersubunit interactions contribute to coupled protein-DNA conformational changes that lead to sequential activation and reciprocal inhibition of pairs of active sites in the recombinase tetramer during recombination.