Host range deletion mutant of vaccinia virus defective in human cells

Abstract

A vaccinia virus host range (hr) mutant unable to multiply in most human cell lines assayed has been isolated after nitrous acid mutagenesis. This mutant also displayed various alterations in plaque morphology and cytopathic effect on permissive cell lines. The block in multiplication in human cells was at an early stage of infection. Only early cytoplasmic RNA and early viral-induced polypeptides could be detected and there was no evidence of morphological events within viroplasms. Protein synthesis constantly declined as infection proceeded suggesting either that early viral mRNA was unstable or that the mutant virus was defective in a step necessary for the maintenance of translation. Restriction enzyme digestion of DNA from the hr mutant revealed that it was deleted of about 12.6 × 10 6 daltons in the left-hand end of the genome leaving intact a fragment containing the terminal crosslink. In both permissive and nonpermissive cells the mutant failed to induce the synthesis of an early 42K polypeptide which could thus be encoded within a region of the deleted sequence. The failure to segregate the various phenotypic and biochemical properties of the hr mutant from one another through recombination with a temperature sensitive mutant indicated that the pleiotropic characteristics of the mutant virus were due to the deletion.