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.