Identification of two novel TAF subunits of the yeast Saccharomyces cerevisiae TFIID complex

Using a combination of ion exchange and immunoaffinity chromatography we ha ve purified the general transcription initiation factor TFIID to near homog eneity from Saccharomyces cerevisiae. Yeast TFIID is composed of TBP, the T ATA box binding protein, and 14 distinct TSP-associated factors (TAFs), whi ch range in size from 17 to 150 kDa. Twelve of the TAF subunits have been p reviously identified, but two, TAF48p and TAF65p, are novel. TAF48p exhibit s significant sequence similarity to the conserved C-terminal region of Dro sophila TAF110p, human TAF130p, and human TAF105p and is encoded by a previ ously identified gene MPT1. TAF65p shows no significant sequence homology t o any previously identified TAFp, The genes encoding TAF48p and TAF65p are single copy and essential for normal yeast cell growth. Furthermore, neithe r TAF48p nor TAF65p are associated with the histone acetylase Spt-Ada-Gcn5 complex or other non-TFIID TBF TAF complexes. The significance of these res ults in terms of TFIID structure, function, and organization is discussed.