Cooperativity mutants of the gamma delta resolvase identify an essential interdimer interaction

gamma delta resolvase, a transposon-encoded site-specific recombinase, catalyzes the resolution of the cointegrate intermediate of gamma delta transposition. The recombination reaction involves the formation of a catalytic nucleoprotein complex whose structure is determined by specific protein-DNA and protein-protein interactions. We have isolated many resolvase mutants and have identified four that are unable to mediate a subclass of higher order protein-protein interactions necessary for recombination. This mutant phenotype is characterized by an inability to catalyze recombination, a loss of cooperative binding to res DNA, and a failure to induce looping out of the DNA between two resolvase binding sites within res. The amino acid side chains identified by the cooperativity mutants cluster on a surface of the protein that mediates an interaction between resolvase dimers in a crystallographic tetramer. We have therefore identified a region of resolvase that mediates an interdimer protein-protein interaction necessary for the formation of the recombinogenic synaptic intermediate.