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. 2010 Jun;22(3):374-82.
doi: 10.1016/j.ceb.2010.03.005. Epub 2010 Apr 2.

Multiple faces of the SAGA complex

Evangelia Koutelou  1 , Calley L Hirsch, Sharon Y R Dent
Affiliations

Multiple faces of the SAGA complex

Evangelia Koutelou et al. Curr Opin Cell Biol. 2010 Jun.

Abstract

The SAGA complex provides a paradigm for multisubunit histone modifying complexes. Although first characterized as a histone acetyltransferase, because of the Gcn5 subunit, SAGA is now known to contain a second activity, a histone deubiquitinase, as well as subunits important for interactions with transcriptional activators and the general transcription machinery. The functions of SAGA in transcriptional activation are well-established in Saccharomyces cerevisiae. Recent studies in S. pombe, Drosophila, and mammalian systems reveal that SAGA also has important roles in transcript elongation, the regulation of protein stability, and telomere maintenance. These functions are essential for normal embryo development in flies and mice, and mutations or altered expression of SAGA subunits correlate with neurological disease and aggressive cancers in humans.

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Figures

Figure 1
Figure 1
The enzymatic activities of SAGA facilitate transcription. Different modules of SAGA are required for various stages of gene activation. A. The recruitment module localizes the SAGA complex to target genes, via an activator protein, allowing the HAT module to acetylate neighboring histones. B. The TBP interaction module strengthens SAGA interactions with the transcriptional machinery and phosphorylation (P) of the Pol II CTD at Ser5 allows transcription to proceed. C. Upon initiation, SAGA is recruited to the Pol II machinery and assists in elongation, promoting further acetylation of histones within the coding region and the Dub module deubiquitinates histones H2B. D. Deubiquitinated histones allow the interaction of Ctk1 with H2B, which phosphorylates Ser2 of the Pol II CTD to extend transcriptional elongation. Some of the questions remaining in this process include: A. Can other SAGA components (X) also contribute to HAT activity? B. Do PTMs (*) also regulate aspects of SAGA module interactions and activities? C. Does histone acetylation have any effect on SAGA Dub activity? C, D. Can the HAT module control Dub activity and vice versa?
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