CIF150, A HUMAN COFACTOR FOR TRANSCRIPTION FACTOR IID-DEPENDENT INITIATOR FUNCTION

The transcription factor IID (TFIID) complex is highly conserved betwe en the Drosophila and mammalian systems. A mammalian homolog has been described for all the Drosophila TATA box-binding protein-associated f actors (TAFs), with the exception of dTAF(II)150. We previously report ed the identification of CIF, an essential cofactor for TFIID-dependen t transcription from promoters containing initiator (Inr) elements. He re we describe the molecular cloning of CIF150, the human homolog of d TAF(II)150, and present biochemical evidence that this factor is invol ved in Inr activity. CIF150 is capable of mediating TFIID-dependent In r activity in a complementation assay, and a protein fraction lacking Inr activity lacks detectable amounts of CIF150. Despite the striking similarity to dTAF(II)158, CIF150 does not appear to be associated wit h human TFIID. However, in vitro binding assays revealed a specific an d direct interaction between CIF150 and hTAF(II)135. This interaction might be structurally important for the functional interaction between CIF150 and human TFIID, since CIF150 stabilizes TFIID binding to a co re promoter.