acetylation in combination with other histone modiﬁcations at the GAL1 and ADH1 promoters may contribute to the role of chromatin structure in PIC formation and hence transcriptional activation. Histones are evicted during active transcription in vivo (37). Since Sgf73p is required for formation of the PIC assembly (and hence transcriptional activation), histone evic- tion from the SAGA-dependent promoters would thus be sig- niﬁcantly reduced in Dsgf73. Indeed, our study demonstrates the elevated levels of histone H3 at the SAGA-dependent promoters in the absence of Sgf73p. Thus, impairment of PIC formation in Dsgf73 decreases histone H3 eviction and hence alters chromatin structure at the SAGA-dependent promoters. In summary, we provide evidence that Sgf73 is a component of the SAGA complex in vivo, consistent with previous biochemical data (9,10). Sgf73p regulates SAGA recruitment, and is required for the assembly of PIC at the core promoters of the SAGA-dependent genes. However, formation of the PIC assembly at the core promoters is differ- entially regulated by histone H3 acetylation or Gcn5p-HAT activity of SAGA. Further, impairment of PIC formation in Dsgf73 lowers histone H3 eviction from the SAGA-dependent promoters, and thus alters chromatin structure. These results provide valuable information on the functional role of yeast Sgf73p (and possibly human ataxin-7 or Sca7p) in regulation of gene expression in vivo. ACKNOWLEDGEMENTS We thank Michael R. Green for TBP and TAF antibodies; Fred Winston for yeast strains; and Praveena Krishnan and Kathy Yee for technical assistance. This work was supported by a National Scientist Development Grant (0635008N) from American Heart Association, a Research Scholar Grant (06–52) from American Cancer Society, three Central Research Committee Grants from SIU School of Medicine, a Faculty Seed Grant from SIU Office of Research Development and Administration, an RFA Grant from SIU Cancer Institute, and a start-up fund from SIU School of Medicine. Funding to pay the Open Access publication charges for this article was provided by the Department of Biochemistry and Molecular Biology of SIU School of Medicine. Conflict of interest statement. None declared. REFERENCES 1. Lee,T.I., Causton,H.C., Holstege,F.C., Shen,W.C., Hannett,N., Jennings,E.G., Winston,F., Green,M.R. and Young,R.A. (2000) Redundant roles for the TFIID and SAGA complexes in global transcription. Nature, 405, 701–704. 2. Roberts,S.M. and Winston,F. 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