Analysis of a nucleoprotein complex: the synaptosome of gamma delta resolvase.

The gamma delta resolvase protein is one of a large family of transposon-encoded site-specific recombinases. It performs recombination in a DNA-protein complex that contains 12 resolvase protomers and two copies of the 120-base pair DNA substrate, res (each with three binding sites for a resolvase dimer). A derivative of resolvase with altered DNA binding specificity was used to show that the role of resolvase at site I, which contains the crossover point, differs from its role at the other two binding sites. The resolvase dimers that initially bind to site I are the only ones that require the residue Ser10, essential for catalysis of DNA breakage. In addition, these site I-bound dimers do not use a specific interaction between dimers that is required elsewhere in the complex for synapsis of the res sites.