Abstract
TFIIA is an important positive regulator of TFIID, the primary promoter recognition factor of the basal RNA polymerase II transcription machinery. TFIIA antagonises negative TFIID regulators such as negative cofactor 2 (NC2), promotes specific binding of the TBP subunit of TFIID to TATA core promoter sequence elements and stimulates the interaction of TBP-associated factors (TAFs) in the TFIID complex with core promoter elements located downstream of TATA, such as the initiator element (INR). Metazoan TFIIA consists of 3 subunits, TFII alpha (35 kDa), beta (19 kDa) and gamma (12 kDa). TFII alpha and beta subunits are encoded by a single gene and result from site-specific cleavage of a 55 kDa TFIIA (alpha/beta) precursor protein by the protease Taspasel. Metazoan cells have been shown to contain variable amounts of TFIIA (55/12 kDa) and Taspasel-processed TFIIA (35/19/12 kDa) depending on cell type, suggesting distinct genespecific roles of unprocessed and Taspasel-processed TFIIA. How precisely Taspasel processing affects TFIIA functions is not understood. Here we report that Taspasel processing alters TFIIA interactions with TFIID and the conformation of TFIID/TFIIA promoter complexes. We further show that Taspasel processing induces increased sensitivity of TFIID/TFIIA complexes to the repressor NC2, which is counteracted by the presence of an INR core promoter element. Our results provide first evidence that Taspasel processing affects TFIIA regulation of TFIID and suggest that Taspasel processing of TFIIA is required to establish INR-selective core promoter activity in the presence of NC2.