Inhibition of host transcription by vesicular stomatitis virus involves a novel mechanism that is independent of phosphorylation of TATA-binding protein (TBP) or association of TBP with TBP-associated factor subunits

The matrix (M) protein of vesicular stomatitis virus (VSV) is a potent inhi bitor in vivo of transcription by all three host RNA polymerases (RNAP), In the case of host RNA polymerase II (RNAPII), the inhibition is due to lack of activity of the TATA-binding protein (TBP), which is a subunit of the b asal transcription factor TFIID, Despite the potency of M protein-induced i nhibition in vivo, experiments presented here show that M protein cannot di rectly inactivate TFIID in vitro. Addition of M protein to nuclear extracts from uninfected cells did not inhibit transcription activity, indicating t hat the inhibition is indirect and is mediated through host factors. The ho st factors that are known to regulate TBP activity include phosphorylation by host kinases and association with different TBP-associated factor (TAF) subunits. However, TBP in VSV-infected cells was found to be assembled norm ally with its TAF subunits, as shown by ion exchange high-pressure liquid c hromatography and sedimentation velocity analysis. A normal pattern of phos phorylation of TBP in VSV-infected cells was also observed by pH gradient g el electrophoresis. Collectively, these data indicate that M protein inacti vates TBP activity in RNAPII dependent transcription by a novel mechanism, since the known mechanisms for regulating TBP activity cannot account for t he inhibition.