Abstract
Two strains of Escherichia coli K12, C600, and DG163, in which the origins and directions of DNA replication had been mapped previously, were made lysogenic for lambda and lambdai434. The origins of replication in these lysogenic strains were located with respect to the prophage location by chromosome alignment and subsequent hybridization of (3)H-labeled lambda vir DNA with newly replicated and "old" DNA. The results obtained are consistent with similar origins of replication observed in the nonlysogenic strains. These findings suggest that DNA replication in these cells is under the control of the E. coli chromosomal replicon and is independent of the presence of the lambda replicon as predicted by the Jacob, Brenner, and Cuzin model of DNA replication.