Redundant roles for the TFIID and SAGA complexes in global transcription

The transcription factors TFIID and SAGA are multi-subunit complexes involv ed in transcription by RNA polymerase II1,2. TFIID and SAGA contain common TATA-binding protein (TBP)-associated factor (TAF(II)) subunits and each co mplex contains a subunit with histone acetyltransferase activity(3). These observations have raised questions about whether the functions of the two c omplexes in vivo are unique or overlapping. Here we use genome-wide express ion analysis to investigate how expression of the yeast genome depends on b oth shared and unique subunits of these two complexes. We find that express ion of most genes requires one or more of the common TAF(II) subunits, indi cating that the functions of TFIID and SAGA are widely required for gene ex pression. Among the subunits shared by TFIID and SAGA are three histone-lik e TAF(II)s, which have been proposed to forma sub-complex and mediate a com mon function in global transcription. Unexpectedly, we find that the histon elike TAF(II)s have distinct roles in expression of the yeast genome. Most importantly, we show that the histone acetylase components of TFIID and SAG A (TAF(II)145 and Gcn5) are functionally redundant, indicating that express ion of a large fraction of yeast genes can be regulated through the action of either complex.