Abstract
Purified vaccinia virus was irradiated by γ-rays under direct-effect conditions. The ability of the irradiated samples to form plaques (infectivity) and to induce viral DNA synthesis was determined. The radiosensitive volume of the viral unit causing infection (1.9 x 10-17 cm.3) is very small compared with the volume of the whole viral DNA ( 10%).
The inactivation of the DNA replication function follows a simple exponential law. The radiosensitive volume necessary for the replication of DNA (1.6 x 10-18 cm.3) represents only 8.5% of the DNA necessary for infectivity and 0.85% of the total viral DNA. This indicates existence of a dissociation between two functions of vaccinia virus, the synthesis of viral DNA and infectivity.