A study of F episome replication in Escherichia coli.

The amount of F lac spisomal DNA present in an E. coli K12 F lac strain was measured as a percentage of total DNA at a number of growth rates by DNA/DNA hybridisation with DNA from a strain of Protsus mirabilis carrying the same F lac particle. The rate of change in average mass par call and average DNA content par call were Measured as a function of growth rats. The spisomal DNA was extracted as superhelical circles and the molecular weight measured from the contour length as seen under the electron microscope. Simple mathematical expressions were derived to interpret these data in terms of the time of replication of the episome relative to the time of initiation of chromosome repilaction, with two copies of the episome per chromosome terminus. Present models do not account than that to which the chromosome initiation is coupled end a new model is proposed.