R46 encodes a site-specific recombination system interchangeable with the resolution function of Tn A

Abstract

Transposition of Tn A onto the IncN plasmid R46 generates unstable DNA molecules. The R46::Tn A recombinant plasmids undergo further DNA rearrangements which depend on the orientation in which the Tn A element is inserted into the plasmid, and deletions and inversions of R46 and Tn A sequences have been observed. Both types of rearrangement have the same specific endpoints, one within Tn A and one located between the R46 coordinates, 36.0 and 37.0. The results are consistent with the operation of a recA-independent, site-specific recombination system utilizing, at least in part, the transposon cointegrate resolution system of Tn A, together with R46-encoded functions. Data are presented that indicate that R46 encodes analogs of both the res site of Tn A and its tnpR gene, although little homology between this element and the plasmid is apparent. Models for the Tn A-induced generation of site-specific deletions and inversions upon transposition of Tn A to R46 are presented.