Inactivation of prophage in ultraviolet-irradiated Escherichia coli: dependence on recA gene activity.

The fate of the prophage part of the lysogenic chromosome was followed in the course of post-ultraviolet incubation. For this purpose, lambda cI857 ind prophage, which can be induced by heat but not by ultraviolet light, was used. The prophage, intially more resistant than its repair-proficient host cell, was rapidly inactivated. This inactivation was not caused by the impaired capacity of irradiated cells to support growth of the phage. Over the entire dose range tested, little, if any, sensitivity difference between the host and the prophage was found at the end of cell division delay. Rapid inactivation of the prophage was also observed in uvr cells after small doses of ultraviolet light. The same small doses did not cause inactivation in lysogens carrying a mutation in the gene recA. This suggests that the functional gene recA is required for inactivation of the prophage part of the lysogenic chromosome.