Isolation of Temperature-Sensitive Mutants of Bombyx mori Nuclear Polyhedrosis Virus

Six temperature-sensitive mutants (designated TS1—TS6) of Bombyx mori nuclear polyhedrosis virus (BmNPV) were isolated and three were characterized. In BmN4 cells infected with each ts mutant, occlusion bodies were produced normally, but extracellular virus was produced in reduced amounts at 33°C. The ts mutant adsorption properties of TS3 were similar to the wild type but TS1 and TS2 showed lower levels. SDS-PAGE analysis showed that some polypeptides synthesized in the cells infected with TS2 and TS3 were different from those of the wild type virus. In these ts mutants, such alterations did not depend on the incubation temperature of cultured cells. Restriction endonuclease analysis of viral DNA of ts mutants suggested that most of the mutations occurred in the regions where homologous regions of BmNPV were localized, and the positions of these regions on the genome were similar to those of AcMNPV ts mutants.