TBP BINDS THE TRANSCRIPTIONALLY INACTIVE TA(5) SEQUENCE BUT THE RESULTING COMPLEX IS NOT EFFICIENTLY RECOGNIZED BY TFIIB AND TFIIA

The binding of TBP (TFIID) to the TATA box has been considered to dire ct promoter recognition and preinitiation complex formation because it is the first event leading to basal transcription by RNA polymerase I I, Here, we analyse the binding of yeast TBP to a consensus TATAAA box and two point mutations, TAAAAA (inactive) and TATATA (active). Despi te the fact that the TAAAAA sequence does not support transcription in vitro, yeast TBP binds the three sequences showing, in this sense, on ly a limited sequence specificity, However, the TBP-TAAAAA complex can not be recognised by other basal transcription factors, in particular by TFIIB, DNase I footprinting patterns of the TBP-TAAAAA complex are different from those observed in functional TBP-TATA box complexes, in dicating that, most likely, it is a different spatial arrangement of t he TBP-DNA complex that prevents formation of the TFIIB-TBP-TAAAAA com plex, also seriously impairing entry of TFIIA to the complex, DNA defo rmability of the A/T-rich sequences appears to be an important determi nant in the formation of a productive TBP-TATA complex, These results indicate that the transcriptional competence of A/T-rich sequences is determined not only by TBP binding, but also by the ability of other b asal transcription factors to recognise the preformed TBP-DNA complexe s.