Isolation and basic properties of temperature--sensitive mutants of Venezuelan equine encephalomyelitis virus.

Fifteen temperature-sensitive (ts) mutants were isolated from 4 Venezuelan equine encephalomyelitis virus clones by nitrous acid treatment or by growing the virus in the presence of 5-fluoruracil. Three of them were classified as RNA- mutants by their inability to synthesize RNA at nonpermissive temperature (1.5-3.3% in respect to the wild type). The remaining 11 mutants showed a slight decrease of RNA synthesis at the nonpermissive temperature (32-73+) and were referred to the RNA+ phenotype. One mutant possessed RNA +/- phenotype (18%). Five complementation groups were determined by complementation analysis of the mutants.