Reconstitution of yeast RNA polymerase I transcription in vitro from purified components - TATA binding protein is not required for basal transcription

Five purified protein components, RNA polymerase I, Rrn3p, core factor, TBP (TATA-binding protein), and upstream activation factor, are sufficient for high level transcription in vitro from the Saccharomyces cerevisiae rDNA p romoter. Rrn3p and pol I form a complex in solution that is active in speci fic initiation. Three protein components, pol I, Rrn3p, and core factor, an d promoter sequence to -38, suffice for basal transcription. Unlike pol II and pol III, yeast pol I basal transcription does not require TBP. Instead, TBP, upstream activation factor, and the upstream. element of the promoter together stimulate pol I basal transcription to a fully activated level. T he role of TBP in pol I transcription is fundamentally different from its r ole in pol II or pol III transcription.