Cluster analysis of mass spectrometry data reveals a novel component of SAGA.

The SAGA histone acetyltransferase and TFIID complexes play key roles in eukaryotic transcription. Using hierarchical cluster analysis of mass spectrometry data to identify proteins that copurify with components of the budding yeast TFIID transcription complex, we discovered that an uncharacterized protein corresponding to the YPL047W open reading frame significantly associated with shared components of the TFIID and SAGA complexes. Using mass spectrometry and biochemical assays, we show that YPL047W (SGF11, 11-kDa SAGA-associated factor) is an integral subunit of SAGA. However, SGF11 does not appear to play a role in SAGA-mediated histone acetylation. DNA microarray analysis showed that SGF11 mediates transcription of a subset of SAGA-dependent genes, as well as SAGA-independent genes. SAGA purified from a sgf11 Delta deletion strain has reduced amounts of Ubp8p, and a ubp8 Delta deletion strain shows changes in transcription similar to those seen with the sgf11 Delta deletion strain. Together, these data show that Sgf11p is a novel component of the yeast SAGA complex and that SGF11 regulates transcription of a subset of SAGA-regulated genes. Our data suggest that the role of SGF11 in transcription is independent of SAGA's histone acetyltransferase activity but may involve Ubp8p recruitment to or stabilization in SAGA.