MU TRANSPOSITIONAL RECOMBINATION - DONOR DNA CLEAVAGE AND STRAND TRANSFER IN TRANS BY THE MU TRANSPOSASE

Central to the Mu transpositional recombination are the two chemical s teps; donor DNA cleavage and strand transfer. These reactions occur wi thin the Mu transpososome that contains two Mu DNA end segments bound to a tetramer of MuA, the transposase. To investigate which MuA-monome r catalyzes which chemical reaction, we made transpososomes containing wild-type and active site mutant MuA. By preloading the MuA variants onto Mu end DNA fragments of different length prior to transpososome a ssembly, we could track the catalysis by MuA bound to each Mu end segm ent. The donor DNA end that underwent the chemical reaction was identi fied. Both the donor DNA cleavage and strand transfer were catalyzed i n trans by the MuA monomers bound to the partner Mu end. This arrangem ent explains why the transpososome assembly is a prerequisite for the chemical steps.