Mutants of Sindbis Virus I. Isolation and Partial Characterization of 89 New Temperature-Sensitive Mutants

Abstract

More than 100 new temperature-sensitive mutants of Sindbis virus have been isolated, following mutagenesis with nitrous acid, N-methyl-N’-nitro-N-nitrosoguanidine, Sazacytidine, and 5-fluorouridine. Thirty-six of these mutants synthesize at least 60% as much RNA at the nonpermissive temperature as does the parental strain and are designated RNA+; 23 mutants synthesize between 10 and 60% as much RNA as the parental strain at 40° and are designated RNA±; 30 mutants make less than 10% as much RNA at 40° and are called RNA-. The remaining mutants have not been tested for RNA incorporation. The thermal stability at 56° of most of the mutant particles has been examined. The majority of the RNA+ mutants is more sensitive to heating at 56° than the parental HR strain, and RNA+ mutations appear to reside primarily in genes coding for the structural proteins. Approximately 20% of either RNA± or RNA- mutants are thermosensitive, and these mutations thus appear to reside primarily in genes coding for the nonstructural proteins. Complementation assays have been performed with a number of these mutants and with those of Burge and Pfefferkorn (1966a, b). The existence of three complementation groups among the RNA+ mutants, which appear to encode the three major structural proteins, has been confirmed; no new complementation groups among RNA+ mutants have been identified. A total of four complementation groups has been identified among the RNA- mutants. Thus, Sindbis virus contains at least seven complementation groups.