Host cell
RNA polymerase II (Pol II)-mediated transcription is inhibited by poliovirus
infection. This inhibition is correlated to a specific decrease in the activity of a chromatographic fraction which contains the
transcription factor TFIID. To investigate the mechanism by which poliovirus
infection results in a decrease of
TFIID activity, we have analyzed a component of
TFIID, the
TATA-binding protein (
TBP). Using Western immunoblot analysis, we show that
TBP is cleaved in poliovirus-infected cells at the same time postinfection as when Pol II transcription is inhibited. Further, we show that one of the cleaved forms of
TBP can be reproduced in vitro by incubating
TBP with cloned, purified poliovirus encoded
protease 3C.
Protease 3C is a poliovirus-encoded
protease that specifically cleaves
glutamine-
glycine bonds in the viral
polyprotein. The cleavage of
TBP by
protease 3C occurs directly. Finally, incubation of an uninfected cell-derived
TBP-containing fraction (
TFIID) with
protease 3C results in significant inhibition of Pol II-mediated transcription in vitro. These results demonstrate that a cellular
transcription factor can be directly cleaved both in vitro and in vivo by a viral
protease and suggest a role of the poliovirus
proteinase 3C in host cell Pol II-mediated transcription shutoff.