Genetic Analysis of a Baculovirus, Autographa californica Nuclear Polyhedrosis Virus I. Isolation of Temperature-Sensitive Mutants and Assortment into Complementation Groups

Abstract

Temperature-sensitive ( ts ) mutants were isolated from the baculovirus Autographa californica (alfalfa looper) M NPV, grown in Spodoptera frugiperda (fall armyworm) cells in the presence of N -methyl- N′ -nitro- N -nitrosoguanidine. Of 567 plaque isolates screened, 27 were temperature sensitive ( ts ), representing a mutation frequency of 4.8%. Ten ts mutants were studied in detail: six failed to yield nonoccluded virus at 33°C ( NOV mutants), whereas the other four produced nonoccluded virus but were restricted in formation of polyhedra at 33°C ( Poly mutants). One of the six NOV mutants failed to synthesize viral DNA. Reversion and leak frequencies were determined, and the mutants were assorted into complementation groups based on the yield of polyhedrin synthesis in cells coinfected with pairs of mutants at 33°C, as measured by radioimmunoassay. For NOV mutants, complementation indexes were also based on virus yield and were consistent with those based on polyhedrin synthesis. Nine mutants were assorted into five complementation groups. One mutant remained unclassified.