ASPECTS OF THE ULTRAVIOLET PHOTOBIOLOGY OF SOME T-EVEN BACTERIOPHAGES

Bacteriophage T4 DNA metabolism is largely insulated from that of its host, although some host functions assist in the repair of T4 DNA dama ge. Environmental factors sometimes affect survival and mutagenesis af ter ultraviolet (UV) irradiation of T4, and can affect mutagenesis in many organisms. We therefore tested the effect of certain environmenta l factors and host genetic defects upon spontaneous and UV- induced mu tagenesis and survival in T4 and some related T-even phages. Plating a t pH 9 enhances UV resistance in T4 by about 14% compared to pH 7. The host cAMP regulatory system affects host survival after UV irradiatio n but does not affect T4 survival. Thermal rescue, the increasing surv ival of irradiated T4 with increasing plating temperature, occurs also in phage T6, but only weakly in phages T2 and RB69; this temperature effect is not altered by supplementing infected cells with additional Holliday resolvase (gp49) early in infection. Phage RB69 turns out to have almost 50% greater UV resistance than T4, but has a genome of abo ut the same size; RB69 is UV-mutable but does not produce r mutants, w hich are easily seen in T2, T4, and T6. Spontaneous mutagenesis in T4 shows no dependence on medium and little dependence on temperature ove rall, but mutation rates can increase and probably decrease with tempe rature at specific sites. UV mutagenesis is not affected by incubating irradiated particles under various conditions before plating, in cont rast to phage S13.