Recovery of host cell protein synthesis during infection with a temperature-sensitive mutant of Newcastle disease virus.

When chick embryo fibroblasts infected with high multiplicities of a non-revertible temperature-sensitive (ts) mutant (ts53) of Newcastle disease virus (NDV) at the permissive temperature (34 degrees C) and incubated to allow the appearance of virus-induced proteins were shifted up to and incubated at the non-permissive temperature (42 degrees C), analysis of [3H]leucine-labelled proteins by SDS-PAGE revealed a marked increase in cellular protein synthesis and a decline in viral synthesis, with an eventual return to an apparently uninfected state. Mutant ts53 apparently ceased to suppress cellular protein synthesis, and translation of viral proteins was markedly inhibited. This was not observed in ts+-infected cells, or in ts53-infected cells maintained at the permissive temperature. Recovery from the infected state was inhibited by actinomycin D at any stage, but was not prevented by cycloheximide present immediately before and during temperature shift-up. Mutant ts53 was shown to be RNA- at 42 degrees C, although viral mRNAs synthesized at 34 degrees C are shown to be present throughout host recovery but in an inactive state.