The TATA-binding protein and associated factors are integral components of the RNA polymerase I transcription factor, SL1.

We have previously shown that the TATA-binding protein (TBP) and multiple TBP-associated factors (TAFs) are required for regulated transcriptional initiation by RNA polymerase II. Here we report the biochemical properties of the RNA polymerase I promoter selectivity factor, SL1, and its relationship to TBP. Column chromatography and glycerol gradient sedimentation indicate that a subpopulation of TBP copurifies with SL1 activity. Antibodies directed against TBP efficiently deplete SL1 transcriptional activity, which can be restored with the SL1 fraction but not purified TBP. Thus, TBP is necessary but not sufficient to complement SL1 activity. Analysis of purified SL1 reveals a complex containing TBP and three distinct TAFs. Purified TAFs reconstituted with recombinant TBP complement SL1 activity, and this demonstrates that TBP plus novel associated factors are integral components of SL1. These findings suggest that TBP may be a universal transcription factor and that the TBP-TAF arrangement provides a unifying mechanism for promoter recognition in animal cells.