Bromodomain factor 1 (Bdf1) associates with Saccharomyces cerevisiae TFIID and 
corresponds to the C-terminal half of higher eukaryotic TAF1. It also associates 
with the SWR-C complex, which is important for Htz1 deposition. Bdf1 binds 
preferentially to acetylated histone H4. Bdf1 is phosphorylated, but the 
mechanism and significance of this modification have been unclear. Two distinct 
regions within Bdf1 are phosphorylated; one is just C terminal to the 
bromodomains and the other is near the C terminus. Mutational analysis shows 
that phosphorylation is necessary for Bdf1 function in vivo. Endogenous protein 
kinase CK2 purifies with Bdf1 and phosphorylates both domains. A similar 
mechanism may be responsible for phosphorylation of the C-terminal region of 
mammalian TAF1. These findings suggest that CK2 phosphorylation of Bdf1 may 
regulate RNA polymerase II transcription and/or chromatin structure.