THE UNIVERSAL TRANSCRIPTION FACTOR!
FROM ARCHEA TO HUMANS, TATA OR TATA-LESS, REGARDLESS OF THE RNA POLYMERASE, TBP IS REQUIRED FOR TRANSCRIPTION.
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TBP ROLES IN EUKARYOTIC TRANSCRIPTION:
CLASS I : TBP FUNCTIONS IN THESE PROMOTORS EVEN THOUGH THEY LACK TATA BOXES. TBP IS PART OF THE COMPLEX PROTEIN SL1 ALONG WITH THREE OTHER TBP ASSOCIATED FACTORS (TAFS). SL1 INTERACTS WITH RNA POLYMERASE I TO STRENTHEN ITS BINDING TO THE PROMOTOR AND GIVES SPECIES SPECIFICITY.
CLASS II: IN THIS CLASS TBP IS FOUND WITH 8 TBP ASSOCIATED FACTORS THAT MAKE UP TFIID, WHICH IS JUST ONE OF MANY TRANSCRIPTION FACTORS NECESSARY FOR BASAL TRANSCRIPTION. TATA BOXES ARE USUALLY PRESENT, BUT DO NOT HAVE TO BE- TBP STILL PLAYS A CRITICAL ROLE IN POSITIONING RNA POLYMERASE.
CLASS III: TFIIIB CONTAINS TBP ALONG WITH A SMALL NUMBER OF TBP ASSOCIATED FACTORS. THIS ALLOWS RECRUITMENT AND POSITIONING OF RNA POLYMERASE III NECESSARY TO TRANCRIBE tRANAs AND 5S rRNAs.
TBP, when no TATA box is present, is still critical for transcription through protien-protein interactions. Most of these interactions occur between TATA binding proteins and the C-terminal stirrup of TBP.
For more info on promotors and TBP, visist Dr. J. Scales Molecular Biology Web Page!