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 recognition. Here, we report that purified recombinant TAF(II)250 is a protein serine kinase that selectively phosphorylates RAP74 but not other basal transcription factors or common phosphoacceptor proteins. The phosphorylation of RAP74 also occurs in the context of the complete TFIID complex. Deletion analysis revealed that TAF(II)250 contains two distinct kinase domains each capable of autophosphorylation. However, both the N- and C-terminal kinase domains of TAF(II)250 are required for efficient transphosphorylation of RAP74 on serine residues. These findings suggest that the targeted phosphorylation of RAP74 by TAF(II)250 may provide a mechanism for signaling between components within the initiation complex to regulate transcription.