Abstract
Temperature-sensitive (ts) RNA polymerase mutants of a picornavirus are reported. Two foot-and-mouth disease virus (FMDV) mutants designated ts 22 and ts 115 have been characterized. As judged by isoelectric focusing, both have charge alterations in P56a, the FMDV RNA polymerase protein. Virus RNA synthesis in cells infected with the mutants is severely impaired at the nonpermissive temperature. RNA polymerase purified from baby hamster kidney cells infected with these mutants exhibits a marked ts transcribing activity in vitro. Spontaneous revertants of both mutants have P56a polypeptides that are indistinguishable from the parental proteins on the basis of charge. The revertants regain the ability to synthesize virus RNA in vivo at the nonpermissive temperature. RNA polymerase purified from the revertants remains transcriptionally active at the nonpermissive temperature.