A single DNA-binding transcription factor is sufficient for activation from a distant enhancer and/or from a promoter position

Abstract

Typical cell type-specific or inducible mammalian genes are under the control of one or more remote enhancers which transmit their effect to the promoter region located at the initiation site of transcription. Both enhancers and promoters are composed of multiple binding sites for transcription factors. To study the requirements for promoter and enhancer function, we have used a reporter gene that is completely dependent on a single DNA-binding transcription factor in vivo. This factor is a truncated, hormone-independent form of the glucocorticoid receptor which interacts strongly with a palindromic binding site. After transfection into HeLa cells, transcription of a reporter gene with one, two or four copies of the binding site upstream of the TATA box is enhanced less than 10, at least 100 and greater than 1000-fold respectively, in the presence of the receptor. Even when the TATA box is deleted, the four upstream binding sites confer receptor-dependent transcription, though from scattered initiation sites. When four copies of the palindromic binding site are placed downstream of the transcription unit, they form a very strong receptor-dependent enhancer. This enhancer can activate comparably well promoters containing binding sites for either glucocorticoid receptor, Sp1 factor, or octamer factor. Our data show that a single defined DNA-binding factor can mediate both promoter and enhancer activity, and that it can co-operate functionally both with itself and with seemingly unrelated transcription factors.