A TEMPERATURE-SENSITIVE MUTATION OF THE VACCINIA VIRUS E11 GENE ENCODING A 15-KDA VIRION COMPONENT

The ts49 mutation of vaccinia virus WR was mapped by marker rescue to the E11 gene encoding a 15-kDa polypeptide. During synchronous infecti on of BSC49 cells with wild-type virus, immunoreactive E11 protein acc umulated in parallel with the onset of late protein synthesis. Immunob lotting of extracts of wild-type virions showed that the E11 protein w as encapsidated within the virus core. A normal temporal pattern of vi ral protein synthesis was observed in cells infected with ts49 at the nonpermissive temperature (40 degrees) and normal-appearing ts49 proge ny virions were observed by electron microscopy. Sequencing of the E11 gene of ts49 revealed a single amino acid substitution, Gly(66)Arg, i n the mutant E11 polypeptide. The steady-state level of E11 protein du ring ts49 infection was much lower than that observed during infection with wildtype virus. This was the case at both the permissive and non permissive temperatures. We discuss two possible explanations for the thermosensitive growth of ts49: (i) that virus infectivity requires a threshold level of active E11 protein or (ii) that E11 function is con ditionally essential. (C) 1996 Academic Press, Inc.