Identification of a partition and replication region in the Alcaligenes eutrophus megaplasmid pMOL28

A 4.64 kb region of the 180 kb heavy metal resistance plasmid pMOL28 of Alcaligenes eutrophus CH34, previously shown to be able to replicate autonomously, was sequenced and analyzed. Three genes involved in plasmid maintenance were identified: parA28 and parB28 are involved in plasmid partitioning and stability, while repA28 encodes a protein required for replication. In addition to the par AB28 genes, a third locus, parS28, required in cis active partitioning was identified. The parABS28 locus of pMOL28 shows strong similarity in organization to the sop, par and rep regions, respectively, of the Escherichia coli F-factor, the E.coli P1 and P7 prophages and the Agrobacterium pTiB6S3 and pRiA4b plasmids. The ParAB28 proteins of pMOL28 also show similarity to the proteins encoded by two conserved open reading frames present in the replication regions of the Pseudomonas putida and Bacillus subtilis chromosomes. The functionality of the pMOL28 par region was examined by performing stability and incompatibility tests between pMOL28 and pMOL846 or pMOL850 which contain the 4.64 EcoRI replicon fragment of pMOL28, cloned in opposite orientations into pSUP202, which is itself unable to replicate in A. eutrophus. The RepA2 8 replication protein showed similarity to the RepL protein of P1, which is required for lytic replication of this E. coli phage. The replication origin of pMOL28, oriV28, seems to be located within the repA28 coding region, and pMOL28 replication may depend on transcriptional activation of oriV28.