A model for the gamma delta resolvase synaptic complex.

The serine recombinase gamma delta resolvase performs site-specific recombination in an elaborate synaptic complex containing 12 resolvase subunits and two 114-base pair res sites. Here we present an alternative structural model for the synaptic complex. Resolvase subunits in the complex contact their neighbors in equivalent ways, using three principal interactions, one of which is a newly proposed synaptic interaction. Evidence in support of this interaction is provided by mutations at the interface that either enable resolvase to synapse two copies of site I or inhibit synapsis of complete res sites. In our model, the two crossover sites are far apart, separated by the resolvase catalytic domains bound to them. Thus, recombination would require a substantial rearrangement of resolvase subunits or domains.