ROLE OF TATA BOX SEQUENCE AND ORIENTATION IN DETERMINING RNA-POLYMERASE II III TRANSCRIPTION SPECIFICITY/

Work from a number of laboratories has indicated that the TATA box seq uence can act as a basal promoter element not only for RNA polymerase II (RNAP II) transcription, but also for transcription by RNA polymera se III(RNAP III), We previously reported that, in the absence of other cis-acting elements, the canonical TATA sequence TATAAAAA specificall y supported transcription by RNAP II in an unfractionated Drosophila n uclear extract, whereas the sequence TTTTTATA (the same sequence in re verse orientation) directed RNAP III transcription, We have now examin ed a variety of other TATA box sequences with regard to RNA polymerase selectivity and their ability to support RNAP III transcription, The results have allowed us to rank these TATA box sequences with respect to their relative strengths as RNAP III promoter elements in unfractio nated Drosophila extracts. Further, the data indicate that T residues at positions 2 and 4 of the TATA box appear to be important determinan ts of RNAP III selectivity in this system, whereas A residues at these positions favor RNAP II transcription. Finally, the data suggest that transcription factors TFIID and TFIIIB, although both capable of bind ing a variety of TATA elements, have distinct sequence preferences for recognizing the TATA box and possibly the surrounding DNA.