TEMPERATURE-SENSITIVE MUTANTS WITH LESIONS IN THE VACCINIA VIRUS F10 KINASE UNDERGO ARREST AT THE EARLIEST STAGE OF VIRION MORPHOGENESIS

Vaccinia virus encodes two protein kinases; the B1 kinase is expressed early and appears to play a role during DNA replication, whereas the F10 kinase is expressed late and is encapsidated in virions, Here we report that the F10 kinase gene is the locus affected in a complementation group of temperature-sensitive mutants composed of ts15, ts28, ts54, and ts61. Although these mutants have a biochemically normal phenotype at the nonpermissive temperature, directing the full program of viral gene expression, they fail to form mature virions, Electron microscopic analysis indicates that morphogenesis undergoes arrest at a very early stage, prior to the formation of membrane crescents or immature virions, An essential role for the F10 protein kinase in orchestrating the onset of virion assembly is implied.