SIMIAN-VIRUS-40 LARGE T-ANTIGEN INTERACTS WITH HUMAN TFIIB-RELATED FACTOR AND SMALL NUCLEAR RNA-ACTIVATING PROTEIN COMPLEX FOR TRANSCRIPTIONAL ACTIVATION OF TATA-CONTAINING POLYMERASE-III PROMOTERS

The TATA-binding protein (TBP) is common to the basal transcription fa ctors of all three RNA polymerases, being associated with polymerase-s pecific TBP-associated factors (TAFs). Simian virus 40 large T antigen has previously been shown to interact with the TBP-TAFII complexes, T FIID (B. Damania and J. C. Alwine, Genes Dev. 10:1369-1381, 1996), and the TBP-TAF(I) complex, SL1 (W. Zhai, J. Tuan, and L. Comai, Genes De v. 11: 1605-1617, 1997), and in both cases these interactions are crit ical for transcriptional activation, We show a similar mechanism for a ctivation of the class 3 polymerase III (pol III) promoter for the U6 RNA gene. Large T antigen can activate this promoter, which contains a TATA box and an upstream proximal sequence element but cannot activat e the TATA-less, intragenic VAI promoter (a class 2, pol III promoter) , Mutants of large T antigen that cannot activate pol II promoters als o fail to activate the U6 promoter, We provide evidence that large T a ntigen can interact with the TBP-containing pol III transcription fact or human TFIIB-related factor (hBRF), as well as with at least two of the three TAFs in the pol III-specific small nuclear RNA-activating pr otein complex (SNAPc), In addition, we demonstrate that large T antige n can cofractionate and coimmunoprecipitate with the hBRF-containing c omplex TFIIIB derived from HeLa cells infected with a recombinant aden ovirus which expresses large T antigen, Hence, similar to its function with pol I and pol II promoters, large T antigen interacts with TBP-c ontaining, basal pol III transcription factors and appears to perform a TAF-like function.