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

A single tetramer of Mu transposase (MuA) pairs the recombination sites, cleaves the donor DNA, and joins these ends to a target DNA by strand transfer. Analysis of C-terminal deletion derivatives of MuA reveals that a 30 amino acid region between residues 575 and 605 is critical for these three steps. Although inactive on its own, a deletion protein lacking this region assembles with the wild-type protein. These mixed tetramers carry out donor cleavage but do not promote strand transfer, even when the donor cleavage stage is by-passed. These data suggest that the active center of the transposase is composed of the C-terminus of four MuA monomers; one dimer carries out donor cleavage while all four monomers contribute to strand transfer.