Radiation-Induced Reorientation of Chromosome Replication Sequence: Generality in Escherichia coli; Independence of Prophage or 5-Bromouracil Toxicity

Our previous observation that irradiation with X-rays or ultraviolet light induces an altered chromosome replication sequence in Escherichia coli strain 15 T⁻(555-7) has been extended to additional strain, B/r and C. Since strains B/r and C showed no evidence of inducible prophage when examined by the same procedures that previously showed strain 15 T⁻(555-7) to be lysogenic, we conclude that postirradiation alteration of chromosome replication sequence is not related to induction of prophage by radiation. The accuracy of measuring replication sequence by 5-bromouracil density labeling was determined by experiments in which density labeling was accomplished with13 C and15 N. An inhibitory effect of 5-bromouracil on DNA synthesis was observed to a variable extent in the strains studied. Postirradiation inhibition of the rate and extent of total DNA replication by 5-bromouracil also varied according to strain, but the replication sequence observed after irradiation was shown to be accura...