Analysis of Tn7 transposition.

Five gene products required for Tn7 transposition were identified using genetic complementation tests. Four of these (tnsA, tnsB, tnsC and tnsD) are essential for insertion into the attachment site, whereas the fifth (tnsE) is required for transposition to plasmids which lack this site. tnsD is not required for transposition to plasmids lacking the attachment site. This analysis used a chloramphenicol-resistant 'mini' transposon containing Tn7 termini but no complete Tn7 gene product and several compatible expression vectors containing cloned Tn7 fragments. The use of transcriptional and translational fusions allowed the identification of two promoters (P1 and P2) at the righthand end of the transposon and indicated that at least tnsA, tnsB and tnsC are translated in the same direction. Expression from P1 appears to be repressed by tnsB.