REACTIVATION OF PROTEASE-INACTIVATED VACCINIA VIRUS BY HOMOLOGOUS AND MUTANT VIRUSES*

Abstract
Limited inactivation of vaccinia virus by a bacterial protease, "Nagarse", was investigated. A possibility of genetic inhomogeneity of virus population concerning enzyme sensitivity was excluded by the fact that ten serial passages on CAM of the survivors of the enzyme treatment at every passage failed to select any enzyme-resistant virus. Inoculation of Nagarse-inactivated DIE virus with UV-inactivated homologous or mutant virus, DIs strain, onto CAM resulted in a increase of infectivity by about 1.0 to 1.5 log10, which was proved to be controlled by the temperature and the duration of incubation of the mixture before inoculation. A linear relation between the amount of reactivated infectivity and the concentration of UV-inactivated virus was also demonstrated. The data suggest that this reactivation was mediated by a process that occurred in the suspending medium. It was revealed that Nagarse-inactivated virus was reactivated and that reactivating UV-inactivated virus gave no genetic information. Sonic vibration of the Nagarse inactivated virus before inoculation resulted in a decrease of infectivity, suggesting that the limited inactivation of vaccinia virus by Nagarse was accounted for, at least partly, by the reactivation of inactivated virus, probably due to the aggregation of virus particles.