A SUBSET OF TAF(II)S ARE INTEGRAL COMPONENTS OF THE SAGA COMPLEX REQUIRED FOR NUCLEOSOME ACETYLATION AND TRANSCRIPTIONAL STIMULATION

A number of transcriptional coactivator proteins have been identified as histone acetyltransferase (HAT) proteins, providing a direct molecu lar basis for the coupling of histone acetylation and transcriptional activation. The yeast Spt-Ada-Gcn5-acetyltransferase (SAGA) complex re quires the coactivator protein Gcn5 for HAT activity. Identification o f protein subunits by mass spectrometry and immunoblotting revealed th at the TATA binding protein-associated factors (TAF(II)s) TAF(II)90, - 68/61, -60, -25/23, and -20/17 are integral components of this complex . in addition, TAF(II)68 was required for both SAGA-dependent nucleoso mal HAT activity and transcriptional activation from chromatin templat es in vitro. These results illustrate a role for certain TAF(II) prote ins in the regulation of gene expression at the level of chromatin mod ification that is distinct from the TFIID complex and TAF(II)145.