RNA-POLYMERASE II III TRANSCRIPTION SPECIFICITY DETERMINED BY TATA BOX ORIENTATION/

The TATA box sequence in eukaryotes is polymerase II (pol II) and some genes transcribed by RNA polymerase III (pol III), The TATA box is re cognized in a sequence-specific manner by the TATA box-binding protein (TBP), an essential factor involved in the initiation of transcriptio n by all three eukaryotic RNA polymerases. We have investigated the re cognition of the TATA box by the pol II and pol III basal transcriptio n machinery and its role in establishing the RNA polymerase specificit y of the promoter, Artificial templates were constructed that containe d a canonical TATA box as the sole promoter element but differed in th e orientation of the 8-bp TATA box sequence, As expected, pol II initi ated transcription in unfractionated nuclear extracts downstream of th e ''forward'' TATA box, In distinct contrast, transcription that initi ated downstream of the ''reverse'' TATA box was carried out specifical ly by pol III. Importantly, this effect was observed regardless of the source of the DNA either upstream or downstream of the TATA sequence, These findings suggest that TBP may bind in opposite orientations on pol II and pol III promoters and that opposite, yet homologous, surfac es of TBP may be utilized by the pol II and pol III basal machinery fo r the initiation of transcription.