Organization and dynamics of the Mu transpososome: recombination by communication between two active sites

Movement of transposable genetic elements requires the clevage of each end of the element genome and the subsequent joining of these cleaved ends to a new target DNA site. During Mu transposition, these reactions are catalyze d by a tetramer of four identical transposase subunits bound to the paired Mu DNA ends. To elucidate the organization of active sites within this tetr amer, the subunit providing the essential active site DDE residues for each cleavage and joining reaction was determined. We demonstrate that recombin ation of the two Mu DNA ends is catalyzed by two active sites, where, one a ctive site promotes both cleavage and joining of one Mu DNA end. This activ e site uses all three DDE residues from the subunit bound to the transposas e binding site proximal to the cleavage site on the other Mn DNA end (catal ysis in trans). In addition, we uncover evidence that the catalytic activit y of these two active sites is coupled such that the coordinated joining of both Mu DNA ends is favored during recombination. On the basis of these re sults, we propose that the DNA joining stage requires a cooperative transit ion within the transposase-DNA. complex. The cooperative utilization of act ive sites supplied in trans by Mu transposase provides an example of how mo bile elements can ensure concomitant recombination of distant DNA sites.