DNA replication of IncQ broad-host-range plasmids in gram-negative bacteria.

Bacterial plasmids of Escherichia coli incompatibility group Q (IncQ) are broad-host-range plasmids that are able to proliferate in almost all Gram-negative bacteria. They are small, nonconjugative, and multicopy plasmids. They can be mobilized into many species of Gram-negative bacteria by coresident conjugative plasmids. Plasmids RSF1010, R1162, and R300B have DNAs of a size of 8.7 kb, and are best studied among IncQ plasmids. These plasmids encode by themselves three major proteins essential for the initiation of DNA replication. This makes the plasmid DNA replication less dependent on the DNA replication apparatus of host cells, and leads to promiscuity or a broad host range. Considering the biological features of these plasmids, they are potent DNA cloning vehicles. Moreover, their characteristic DNA replication mechanism that makes IncQ plasmids promiscuous is elaborate, and is an interesting object of scientific studies.