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 r eport that the F10 kinase gene is the locus affected in a complementat ion group of temperature-sensitive mutants composed of ts15, ts28, ts5 4, and ts61. Although these mutants have a biochemically normal phenot ype at the nonpermissive temperature, directing the full program of vi ral gene expression, they fail to form mature virions, Electron micros copic 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 orchestratin g the onset of virion assembly is implied.