INHIBITION OF BASAL TRANSCRIPTION BY POLIOVIRUS - A VIRUS-ENCODED PROTEASE (3C(PRO)) INHIBITS FORMATION OF TBP-TATA BOX COMPLEX IN-VITRO

Host cell RNA polymerase II (pol II)-mediated transcription is inhibit ed by poliovirus infection. We demonstrate here that both TATA- and in itiator-mediated basal transcription is inhibited in extracts prepared from poliovirus-infected HeLa cells. This inhibition can pe reproduce d by incubation of uninfected HeLa cell extracts with purified, recomb inant poliovirus protease, 3C(Pro). Transient-transfection assays demo nstrate that 3C(Pro), in the absence of other viral proteins, is able to inhibit cellular pol II-mediated transcription in vivo. Three lines of evidence suggest that inactivation of TATA-binding protein (TBP) i s the major cause of inhibition of basal transcription by poliovirus. First, RNA pol II transcription in poliovirus-infected cell extract is fully restored by bacterially expressed TBP. Second, addition of puri fied TBP restores transcription in heat-treated nuclear extracts from mock- and virus-infected cells to identical levels. Finally, using a g el mobility shift assay, we demonstrate that incubation of TBP with th e viral protease (3C(Pro)) inhibits its ability to bind TATA sequence in vitro. These results suggest that inhibition of pol II transcriptio n in mammalian cells infected with poliovirus is, at least in part, du e to the inability of modified TBP to bind pol II promoter sequences.