Functioning of the F-plasmid origin of replication in an Escherichia coli K12 Hfr strain during exponential growth.

The pattern of chromosome replication in the Escherichia coli K12 Hfr strain KL99 was investigated during exponential growth by DNA-DNA hybridization. The levels of chromosomal markers close to the point of insertion of F (near pyrC) were raised in relation to other markers by comparison with the situation in an isogenic F- strain. The data are shown to be consistent with the proposal that the integrated F plasmid was regulating its copy number by a mass-titration mechanism.