Characterization of a replicon of the moderately promiscuous plasmid, pGSH5000, with features of both the mini-replicon of pCU1 and the ori-2 of F.

The dominant, polA1-independent replicon of pGSH500, rep beta (1.8 kb), consists of a cis-acting oriV region of 245 bp; a repB gene that is essential for autonomous replication and 18, 30 to 36 bp iterons which constitute the inc/cop region. The molecular organization of rep beta resembles that of mini-pCU1 (IncN). Furthermore, there is a 58% identity between the Rep proteins of these replicons. RepB also shows a 31% identity with RepE of mini-F. In addition, an 80% identity over 200 bp was identified between the cis-acting beta oriV region and the equivalent region of ori-2 (mini-F). Replicons with deletions of repB could be complemented by Rep (pCU1) and RepE (mini-F) in trans, supporting the hypothesis that rep beta is a natural hybrid between a pCU1-like and F-like replicon.