Human TAFII55 (hTAFII55), a component of the general transcription factor TFIID, is the only general transcription factor encoded by an intronless gene identified thus far. Analysis of the TATA-less hTAFII55 promoter-proximal sequence reveals putative binding sites for STAT-1, MEF2, Sp1, AP2, AREB6 and E47. Using chromatin immunoprecipitation, DNase I footprinting and electrophoretic mobility shift assays, we demonstrate that Sp1 and AP2 can bind simultaneously to juxtaposed Sp1- and AP2-binding sites in the hTAFII55 promoter-proximal region and functionally modulate hTAFII55 promoter activity, as evidenced by reporter gene assays performed in transiently transfected human C-33A and insect SL2 cell lines. Interestingly, removal of all the promoter-proximal Sp1-binding sites does not impair the function of the hTAFII55 core promoter. Moreover, a 52-bp DNA fragment containing only the hTAFII55 initiator (Inr) and downstream promoter element (DPE) is able to support Ga14-VP16-mediated activation in vivo and in vitro. Our data suggest that Sp1, although it plays an enhancing role in hTAFII55 gene expression, is not essential for hTAFII55 core promoter activity. Interestingly, mutations introduced at the Inr and DPE differentially affect the selection of transcription start sites, suggesting that these two core promoter elements play a non-redundant role in the function of TATA-less promoters.
ASJC Scopus subject areas