Radiobiological Studies of Vaccinia Virus.

Radiation studies of vaccinia virus were carried out using two types of radiation, Coao gamma rays and ultraviolet light (UVL). When virus particles were irradiated with gamma rays a two-component survival curve was obtained. The capacity of Earle’s L cells to support the growth of vaccinia virus was relatively sensitive to gamma rays. Infectious centres formed by infecting L cells with vaccinia virus were irradiated at various times during the eclipse period of virus growth (the Luria-Latarjet experiment). When irradiated with gamma rays, infectious centres exhibited an initial sensitization to inactivation which persisted for at least 3 hours. At times later than 3 hours after infection the infectious centres became progressively more resistant to inactivation by gamma rays (“stabilization”) ; the survival curves remained almost single-hit throughout the eclipse period. Studies with FUdR, an inhibitor of DNA synthesis, showed little stabilization in the absence of viral DNA synthesis. Free particles of vaccinia virus were inactivated according to single-hit kinetics by UVL. The capacity of L cells to form virus was relatively resistant to UVL. In the Luria-Latarjet experiment using UVL, the survival curves of the infectious centres remained single-hit for the first 3 hours of the eclipse period, with slopes about half that of the survival curve for the free virus. Starting between 3 and 4 hours after infection, the survival curves became multihit, but their slopes remained parallel to the slopes of the survival curves of the early infectious centres. Possible interpretations of these results are discussed.