TARGETING TBP TO A NON-TATA BOX CIS-REGULATORY ELEMENT - A TBP-CONTAINING COMPLEX ACTIVATES TRANSCRIPTION FROM SNRNA PROMOTERS THROUGH THE PSE

In the human small nuclear RNA (snRNA) promoters, the presence of a TA TA box recognized by the TATA box-binding protein (TBP) determines the selection of RNA polymerase Ill over RNA polymerase II. The RNA polym erase II snRNA promoters are, therefore, good candidates for TBP-indep endent promoters. We show here, however, that TBP activates transcript ion from RNA polymerase II snRNA promoters through a non-TATA box elem ent, the snRNA proximal sequence element (PSE), as part of a new snRNA -activating protein complex (SNAP(c)). In contrast to the previously i dentified TBP-containing complexes SL1, TFIID, and TFIIIB, which appea r dedicated to transcription by a single RNA polymerase, SNAP(c) is al so essential for RNA polymerase III transcription from the U6 snRNA pr omoter. The U6 initiation complex appears to contain two forms of TBP, one bound to the TATA box and one bound to the PSE as a part of SNAP( c), suggesting that multiple TBP molecules can have different function s within a single promoter.