Nucleotide sequence and genetic characterization of the novel IncQ-like plasmid pIE1107

The analysis of the complete nucleotide sequence of the small resistance plasmid pIE1107 revealed a close similarity to the well-known IncQ plasmids. Highly conserved replication proteins and nearly identical origins of replication (oriV) suggest equivalent functions in the related replication systems. However, pIE1107 contains two copies of IncQ-oriV-like DNA which are slightly different regarding the iterons. Upon deletion of a silent copy of IncQ-oriV-like DNA the resulting plasmid is fully compatible with IncQ plasmids, indicating that there is no mutual communication between the replication control of the respective replicons. Experiments with cloned oriV DNA strongly suggest that the replication initiation protein of pIE1107 has specialized into the distinct target-iterons of its own oriV which differs only by a few nucleotides from the oriV of IncQ plasmids. Implications from the apparent highly specific protein-DNA recognition and from the incompatibility properties of pIE1107 for the evolution of a family of compatible, IncQ-like plasmids are discussed.