TAF(11)250 IS A BIPARTITE PROTEIN-KINASE THAT PHOSPHORYLATES THE BASAL TRANSCRIPTION FACTOR RAP74

Some TAF subunits of transcription factor TFIID play a pivotal role in transcriptional activation by mediating protein-protein interactions, whereas other TAFs direct promoter selectivity via protein-DNA recogn ition. Here, we report that purified recombinant TAF(II)250 is a prote in serine kinase that selectively phosphorylates RAP74 but not other b asal transcription factors or common phosphoacceptor proteins. The pho sphorylation of RAP74 also occurs in the context of the complete TFIID complex. Deletion analysis revealed that TAF(II)250 contains two dist inct kinase domains each capable of autophosphorylation. However, both the N- and C-terminal kinase domains of TAF(II)250 are required for e fficient transphosphorylation of RAP74 on serine residues. These findi ngs suggest that the targeted phosphorylation of RAP74 by TAF(II)250 m ay provide a mechanism for signaling between components within the ini tiation complex to regulate transcription.