Lethal and Genetic Effects of Radiophosphorus Decay in Bacteriophages SP82G and T7

Summary

Lethal and genetic effects from the decay of incorporated ³²P and ³³P were compared in bacteriophages SP82G (B. subtilis) and T7 (E. coli) stored at −196°C or 4°C during decay. Both phages are substantially less sensitive to the lethal effects of ³³P than to ³²P. Because ³³P has a much lower nuclear-recoil energy, the results suggest that nuclear recoil is an important cause of ³²P lethality for each phage. Lethal ³²P decays in SP82G at either storage temperature appear to correspond to double-strand breaks in DNA. Marker suicide experiments with temperature-sensitive mutants of SP82G indicate two distinct types of lethal lesion resulting from ³²P decays: one causes differential interruption of genetic transfer into the infected cell; the second causes interference with the transfer or expression of all genetic markers equally. Similar radiophosphorus experiments with amber mutants of T7 indicate the occurrence of the same two types of genetic lesion. The existence of the first type provides additional indirect evidence that T7, like SP82G, injects its genome in a unique linear sequence, always starting at the left end of the genetic map.