Location of the site-specific recombination system of R46: a function necessary for plasmid maintenance.

The R46 site-specific recombination system comprises a per (plasmid-encoded recombinase) gene and a site at which the gene product acts, the per site. The two functions have been cloned into pACYC184. They are encoded by sequences within a region of approximately 2 kb on the R46 genome. These R46 sequences are closely related to the site-specific recombination systems of the ampicillin resistance transposons collectively designated TnA. The R46 per function is interchangeable with the tnpR gene product of TnA. Both enzymes can mediate recombination between the related res and per sites in R46::TnA recombinant plasmids to generate site-specific deletions and inversions. Similar DNA rearrangements occur when TnA inserts into pACYC184 derivatives carrying the cloned R46 per functions. Carriage of this site-specific recombination system contributes to the stable maintenance of R46. By converting plasmid dimers to monomers the R46 per functions help to ensure equal partitioning at cell division.