Isolation and characterization of plasmid pSW200 from Erwinia stewartii.

The nucleotide sequence of pSW200 of Erwinia stewartii SW2 was determined. This plasmid is 4367 bp long, consisting of four mobilization genes, mobCABD, and an origin of replication homologous to those of ColE1-type plasmids. The plasmid also contains a region of forty-one 15-bp repeats. Deleting this region does not affect the stability or the copy number when maintained as sole plasmid in the cell. However, the plasmid is rapidly lost when a homoplasmid with the intact repeat region is introduced into the cell. The function of this region may provide pSW200 an advantage in competing with an incompatible plasmid in the cell.