Loss of Adsorption and Injection Abilities in γ-irradiated Phage T1

Abstract

γ-irradiation of phage T1, suspended in 0·1 M histidine, inactivates some capacities of phage and blocks the early steps of infection. Five per cent of the inactivated phages have lesions in the protein coat, either in the head and leading to rupture and release of DNA, or in the tail and affecting adsorption. The host-killing ability is destroyed in 38 per cent of the inactivated phages. The amount of phage DNA injected into the host cell was measured and compared with the loss of plaque-forming ability after γ-irradiation. The chance of the genome becoming injected per lethal hit decreases to 31 per cent. The amount of injected DNA is of the same order as the fraction of phages remaining without double-strand lesions in the DNA, i.e. without double-strand breaks or cross-links. This agreement suggests that only the DNA molecules with intact double strands are injected: a view confirmed by the localization of the major part of double breaks in the non-injected DNA. A partial injection of the damaged phage genome seems less probable for phage T1.