DIVISION-OF-LABOR AMONG MONOMERS WITHIN THE MU-TRANSPOSASE TETRAMER

A single tetramer of Mu transposase (MuA) pairs the recombination site s, cleaves the donor DNA, and joins these ends to a target DNA by stra nd transfer. Analysis of C-terminal deletion derivatives of MuA reveal s that a 30 amino acid region between residues 575 and 605 is critical for these three steps. Although inactive on its own, a deletion prote in lacking this region assembles with the wild-type protein. These mix ed tetramers carry out donor cleavage but do not promote strand transf er, even when the donor cleavage stage is by-passed. These data sugges t that the active center of the transposase is composed of the C-termi nus of four MuA monomers; one dimer carries out donor cleavage while a ll four monomers contribute to strand transfer.