Isolation and characterization of a temperature-sensitive uncoating mutant of pseudorabies virus.

During the course of characterizing a series of temperature-sensitive mutants of pseudorabies virus, we found one (designated tsL) that did not produce cytopathic changes in rabbit kidney cells at the non-permissive temperature (41 degree C). Although the mutant adsorbed to and penetrated the cells in a normal fashion, virus RNA was not synthesized at 41 degree C in the infected cells. However, if the cells were first incubated at the permissive temperature (32 degree C), virus RNA synthesis occurred at the non-permissive temperature. This occurred even if, during the incubation period at 32 degree C, the expression of viral functions was prevented by treatment with an inhibitor of protein synthesis. The DNA in tsL virions did not appear in the cell nucleus at 41 degree C, and full, non-enveloped nucleocapsids could be recovered from the cytoplasm of tsL virus-infected cells. These results show that the nucleocapsids of tsL remain intact at the non-permissive temperature and that tsL is an uncoating mutant.