CLONING OF AN INR-BINDING AND E-BOX-BINDING PROTEIN, TFII-I, THAT INTERACTS PHYSICALLY AND FUNCTIONALLY WITH USF1

The transcription factor TFII-I has been shown to bind independently t o two distinct promoter elements, a pyrimidine-rich initiator (Inr) an d a recognition site (E-box) for upstream stimulatory factor 1 (USF1), and to stimulate USF1 binding to both of these sites. Here we describ e the isolation of a cDNA encoding TFII-I and demonstrate that the cor responding 120 kDa polypeptide, when expressed ectopically, is capable of binding to both Inr and E-box elements. The primary structure of T FII-I reveals novel features that include six directly repeated 90 res idue motifs that each possess a potential helix-loop/span-helix homolo gy, These unique structural features suggest that TFII-I may have the capacity for multiple protein-protein and, potentially, multiple prote in-DNA interactions, Consistent with this hypothesis and with previous in vitro studies, we further demonstrate that ectopic TFII-I and USF1 can act synergistically, and in some cases independently, to activate transcription in vivo through both Inr and the E-box elements of the adenovirus major late promoter, We also describe domains of USF1 that are necessary for its independent and synergistic activation functions .