Our previous studies employing
alpha-amanitin-sensitive
H-9 and resistant Ama 102 mutant host cells demonstrated that polymerase II (Pol II), or a
drug-sensitive component of the
enzyme, is required for replication of vaccinia virus. Evidence was also obtained indicating that transcription from the host genome does not appear to be involved (
Silver et al., 1979;
Silver and
Dales, 1982), suggesting a possible role for Pol II in transcription from the viral genome. This idea is consistent with the present findings, based on immunofluorescence analysis, which revealed that upon
infection Pol II
antigen is mobilized out of the nucleus into discrete cytoplasmic foci. Effects of treating
H-9 rat myoblasts with
alpha-amanitin upon
vaccinia-specific
protein synthesis were also examined. Under the experimental conditions employed, the toxin drastically curtailed in vivo translation into early, late and late-late
proteins without altering the spectrum of
polypeptides produced. By contrast, treatment with the
drug affected, only minimally, the rate of transcription into
viral RNA, whether in vivo or from isolated
vaccinia factories. The
mRNA isolated from infected and treated or untreated cells was translated in a reticulocyte lysate with equal efficiency and general fidelity. This finding suggests that Pol II may be involved in transcription into RNAs related to factors controlling the in vivo translation process. The possible mechanisms for exercising such controls are discussed in relation to factors regulating transcription by host
RNA polymerases from a
viral DNA genome.