Replication of the multicopy mini-R1 plasmid Rsc11 in Escherichia coli K12: Possible nonrandom selection of participants

The kinetics of replication of the multicopy mini-R1 plasmid Rsc11, in the Escherichia coli K12 strain 1100 were determined by density-shift analysis. One generation after the shift, 7% of the plasmid population remained unreplicated, 86% had replicated once, and only 7% twice. Half a generation later the values were 4, 64, and 32%, respectively. This pattern is unlike that previously reported for the Rsc11 progenitor molecule, pKN102 (R1drd19-B2), and other multicopy plasmids, but closely resembles that of the chromosome and therefore suggests that Rsc11 copies are selected nonrandomly for replication. Another interpretation is discussed. Precursor incorporation into plasmid DNA is sharply curtailed upon transition to the stationary phase of growth. It is possible that Rsc11 replication is stringently controlled.