Direction of bacteriophage lambda DNA replication in a thymine requiring Escherichia coli K-12 strain. Effect of thymidine concentration.

The direction of replication was established for the first round of bacteriophage lambda DNA replication in thymine requiring E. coli K-12 cells exposed to different concentrations of thymidine. It was found that a dramatic decrease in the proportion of bidirectionally replicating molecules followed a decrease in the concentration of thymidine. Moreover, the rightward mode of replication appears to be exclusively favored in unidirectionally replicating molecules found at low concentrations of thymidine.