Requirement of a corepressor for Dr1-mediated repression of transcription.

A Dr1-associated polypeptide (DRAP1) was isolated from HeLa cells and found to function as a corepressor of transcription. Corepressor function requires an interaction between DRAP1 and Dr1. Heterodimer formation was dependent on a histone fold motif present at the amino terminus of both polypeptides. Association of DRAP1 with Dr1 results in higher stability of the Dr1-TBP-TATA motif complex and precluded the entry of TFIIA and/or TFIIB to preinitiation complexes. DRAP1 was found to be expressed in all tissues analyzed with higher levels in tissues with a low mitotic index. Analysis of DRAP1 in the developing brain of rat demonstrated undetectable levels of DRAP1 in actively dividing cells but high levels of DRAP1 expression in differentiated non dividing cells. Dr1 was immunodetected in all cells analyzed. A model for DRAP1-dependent, Dr1-mediated repression of transcription is proposed.