Temperature-sensitive regulation system of prophage lambda induction

Abstract

Mutants of the temperate bacteriophage λ of Escherichia coli have been isolated, which have a temperature-sensitive repression system for prophage induction. These mutants can be classified into two types: λts type I which is induced at 28°C in Penassay broth after treatment for ten minutes at 47·5°C in buffer, or at a high temperature during growth; and λts type II which is induced only when the culture is heated at a high temperature during growth. Type I and type II mutations reside in the cistron cI controlling repressor substance (immunity substance) production. The correlation between ultraviolet- and temperature-sensitivity for the induction of λts prophage has been examined. When irradiated with ultraviolet light, bacteria carrying some λts prophage were induced at lower doses than the induction dose of wild-type prophage λ . Others λts prophage retained the ultraviolet sensitivity to induction of wild-type λ . Mutants of phage λ which are more sensitive to induction by ultraviolet irradiation than the wild-type phage yet as heat-stable as the wild type were isolated. These findings indicate that although many λts prophage are induced by a small dose of ultraviolet light, the ultraviolet sensitivity is not necessarily correlated with the temperature sensitivity. Bacterial mutants which suppress the temperature-sensitive characteristic of the system of prophage λts were isolated. They also restored the ultraviolet sensitivity for the prophage induction to the level of the bacteria lysogenic for the wild-type λ . A possible mechanism of heat inactivation of repressors produced by λts prophage is discussed.