Characterization of the replication origin of the myxobacterial self-replicative plasmid pMF1

Thus far, pMF1 is the only endogenous myxobacterial plasmid whose replication mechanism is unclear. In this study, we determined that the plasmid replicates via the theta-mode. The pMF1.14 gene, located in the pMF1.13–pMF1.15 operon (repABC), encodes an essential replication initiation protein that was predicted to have no typical DNA/protein binding motifs but contains rich disordered regions. The pMF1 replication-related essential cis-acting DNA region, approximate 370 bp, was located within pMF1.14, and was found to contain several directly and inverted atypical repeats. The unique characteristics of the pMF1 replicon are suggested to be the reason for its strict narrow host range in Myxococcus cells.

► We determined the replication mode of myxobacterial plasmid pMF1.
► We confirmed the initiation function of the pMF1.14 protein.
► We located the plasmid minimal essential cis-acting region within pMF1.14 ORF.
► We showed the DNA repeats in pMF1 ori to be atypical plasmid iterons.