Bidirectional replication of the chromosome in Escherichia coli.

E. coli cells initiating chromosome replication after release from amino-acid starvation were incubated in [(3)H]thymine of moderate specific activity, followed by incubation in [(3)H]thymine plus [(3)H]thymidine of very high specific activity. The grain tracks produced in autoradiographs of chromosomes were denser on both ends than in the middle. The autoradiographic patterns are, therefore, evidence that replication of the chromosome in E. coli is bidirectional.