Mutants of phage T4 with increased sensitivity to ultraviolet

Abstract

After treatment of phage T4 with nitrous acid, three independent mutants with increased UV sensitivity have been isolated. The survival curves of two of them, both in darkness and under conditions of maximum photoreactivation, are very similar to those of phage T2. Genetic crosses have shown that the mutations had occurred in the v cistron (formerly called u cistron), which controls the differences in UV sensitivity and photoreactivability between T4 and T2; therefore, these two mutants are called v 1 and v 2. The third mutation, producing a sensitivity level intermediate between T4 and T2, concerns a cistron called x which is not closely linked to v and affects UV sensitivity by a still unknown mechanism. In the recombinant v 1 x, the effects are additive, leading to a UV sensitivity considerably higher than that of T2. Thus, there are now available in phage T4 four sensitivity levels, represented by the genotypes v + x + (wild type), v + x, v x +, and v x, with relative sensitivities of 0.45, 0.75, 1.0, and 2.0, respectively. The slopes of the multicomplex survival curves obtained with the different sensitivity types do not show any simple correlation with the slopes of the monocomplex survival curves. Further, the multicomplex curves of the mutants have shoulders considerably lower than those of T4 and T2 wild type.