Abstract
A region of homology within a 2.2 kilobase [kb] segment of [Escherichia coli] plasmids of incompatibility group F I, which is contained in an EcoRI restriction enzyme fragment bearing genes for autonomous replication was mapped. The coordinates of the 2.2 kb segment are 46.4 F-48.6 F on the physical map of the F plasmid. The origin of vegetative replication was mapped at 42.5 F, at which site F has no sequence homology with other group F I plasmids. Plasmids belonging to other incompatibility groups have no homology with the 46.4-48.6 F segment. Possible mechanisms underlying incompatibility are discussed. Incompatibility may be due to either a limitation in a common equipartitioning mechanism or a limitation in a common replication control. In either case the common mechanism is specific for plasmids belonging to a given incompatibility group.