A New Vaccinia Virus Intermediate Transcription Factor

Transcription of the vaccinia virus genome is mediated by a virus-encoded multisubunit DNA-dependent RNA polymerase in conjunction with early-, intermediate-, and late-stage-specific factors. Previous studies indicated that two virus-encoded proteins (capping enzyme and VITF-1) and one unidentified cellular protein (VITF-2) are required for specific transcription of an intermediate promoter template in vitro. We have now extensively purified an additional virus-induced intermediate transcription factor with a native mass of approximately 100 kDa.