Multiple faces of the SAGA complex

Koutelou, Evangelia; Hirsch, Calley L.; Dent, Sharon Y.R.

doi:10.1016/j.ceb.2010.03.005

Cited by 231 publications

(212 citation statements)

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“…The SAGA complex is highly conserved, and its functions are best characterized in yeast (4,9,17,23,35). In addition to acetylating histone H3 via the Gcn5 subunit, SAGA also proteolytically cleaves ubiquitin moieties from histone H2B via the Ubp8 subunit, which is an ortholog of USP22 (13, 47).…”

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confidence: 99%

Ubp8 and SAGA Regulate Snf1 AMP Kinase Activity

Wilson

Koutelou

Hirsch

et al. 2011

Molecular and Cellular Biology

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Posttranslational modifications of histone proteins play important roles in the modulation of gene expression. The Saccharomyces cerevisiae (yeast) 2-MDa SAGA (Spt-Ada-Gcn5) complex, a well-studied multisubunit histone modifier, regulates gene expression through Gcn5-mediated histone acetylation and Ubp8-mediated histone deubiquitination. Using a proteomics approach, we determined that the SAGA complex also deubiquitinates nonhistone proteins, including Snf1, an AMP-activated kinase. Ubp8-mediated deubiquitination of Snf1 affects the stability and phosphorylation state of Snf1, thereby affecting Snf1 kinase activity. Others have reported that Gal83 is phosphorylated by Snf1, and we found that deletion of UBP8 causes decreased phosphorylation of Gal83, which is consistent with the effects of Ubp8 loss on Snf1 kinase functions. Overall, our data indicate that SAGA modulates the posttranslational modifications of Snf1 in order to fine-tune gene expression levels.Ubiquitination of cellular targets regulates many biological processes, from intracellular trafficking to gene expression. Although ubiquitination by ubiquitin (Ub) ligases is widely studied, less is known about subsequent deubiquitination (DUB) of cellular substrates. The identification of genes coding 16 deubiquitinases in the Saccharomyces cerevisiae (yeast) genome and genes coding at least 60 deubiquitinases in the human genome suggests that not only is deubiquitination important but also that deubiquitination may also occur in a substratespecific manner to regulate specific cellular processes. Despite the lack of knowledge of the targets of many of these deubiquitinases, it is known that some of these enzymes impact cellular growth and function (3,21,46). Overexpression of certain deubiquitinases is associated with progression of malignancy in neuroblastomas and a variety of carcinomas, indicating that these enzymes may be oncogenic (27,31,38).USP22, a deubiquitinase associated with the SAGA histone acetyltransferase (HAT) complex, was identified as a member of an 11-gene "death-from-cancer" signature that serves as a predictor of treatment resistance, aggressive growth, and metastasis of human tumors when overexpressed (7,8). The SAGA complex is highly conserved, and its functions are best characterized in yeast (4,9,17,23,35). In addition to acetylating histone H3 via the Gcn5 subunit, SAGA also proteolytically cleaves ubiquitin moieties from histone H2B via the Ubp8 subunit, which is an ortholog of USP22 (13, 47). Ubp8-mediated deubiquitination of histone H2B regulates the expression of target genes by modulating the level of histone H3 lysine 4 methylation, a mark that is associated with active transcription (13). In addition, Ubp8 facilitates the recruitment of the Cterminal domain kinase (Ctk1) to target gene promoters via histone H2B deubiquitination, which facilitates the transition from transcription initiation to elongation (43).Interestingly, recent studies indicate that the functions of USP22 extend beyond histone H2B, as it also deubiquiti...

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Ubp8 and SAGA Regulate Snf1 AMP Kinase Activity

Wilson

Koutelou

Hirsch

et al. 2011

Molecular and Cellular Biology

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“…The SAGA (Spt-Ada-Gcn5 acetyltransferase) complex is a highly conserved transcriptional coactivator (18) that is involved in the transcription of nearly all yeast genes (19,20) and mediates crosstalk between H3K4me3 and histone hyperacetylation. The HAT activity of SAGA resides in a four-protein subcomplex known as the "HAT module" (21,22), which contains the catalytic subunit Gcn5 (23)(24)(25), Ada2, Ada3 (26,27), and Sgf29 (21,28).…”

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Nucleosome competition reveals processive acetylation by the SAGA HAT module

Ringel

Cieniewicz

Taverna

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The Spt-Ada-Gcn5 acetyltransferase (SAGA) coactivator complex hyperacetylates histone tails in vivo in a manner that depends upon histone 3 lysine 4 trimethylation (H3K4me3), a histone mark enriched at promoters of actively transcribed genes. SAGA contains a separable subcomplex known as the histone acetyltransferase (HAT) module that contains the HAT, Gcn5, bound to Sgf29, Ada2, and Ada3. Sgf29 contains a tandem Tudor domain that recognizes H3K4me3-containing peptides and is required for histone hyperacetylation in vivo. However, the mechanism by which H3K4me3 recognition leads to lysine hyperacetylation is unknown, as in vitro studies show no effect of the H3K4me3 modification on histone peptide acetylation by Gcn5. To determine how H3K4me3 binding by Sgf29 leads to histone hyperacetylation by Gcn5, we used differential fluorescent labeling of histones to monitor acetylation of individual subpopulations of methylated and unmodified nucleosomes in a mixture. We find that the SAGA HAT module preferentially acetylates H3K4me3 nucleosomes in a mixture containing excess unmodified nucleosomes and that this effect requires the Tudor domain of Sgf29. The H3K4me3 mark promotes processive, multisite acetylation of histone H3 by Gcn5 that can account for the different acetylation patterns established by SAGA at promoters versus coding regions. Our results establish a model for Sgf29 function at gene promoters and define a mechanism governing crosstalk between histone modifications.T he different patterns of histone posttranslational modifications distributed across the genome are proposed to constitute a "histone code" that orchestrates distinct transcriptional programs by recruiting specific effector proteins (1-4). The phenomenon of histone code "crosstalk," whereby one type of histone modification directs the establishment of another, or through which several histone modifications are recognized in tandem, has emerged as an important and widespread mechanism regulating chromatin-templated processes (5, 6). The multifunctional complexes that activate transcription are thought to mediate crosstalk through "reader" domains that recognize particular chromatin marks as well as through catalytic subunits that deposit or remove histone modifications (5,7,8). As a result, distinct combinations of histone posttranslational modifications that correlate with transcriptional output cluster across the genome (9-11). High levels of histone 3 lysine 4 trimethylation (H3K4me3) and histone H3 hyperacetylation are present at the promoters of actively transcribed genes (9,11,12), and multiple lines of evidence support the existence of regulatory mechanisms coupling the two modifications. Studies using tandem mass spectrometry to sequence whole histone tails have shown that H3K4me3 is highly correlated with hyperacetylation of the same H3 tail (13,14). Deleting the yeast Set1 methyltransferase, which trimethylates H3K4, leads to dramatically lower levels of histone H3 tail acetylation overall (13, 15). These results are consistent with ...

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“…7 Since then, results from our group and many others have shed light on the principles regulating SAGA's ability to coactivate gene expression. 8 Increasingly, however, evidence has indicated that regulation of SAGA in multicellular organisms involves more sophisticated mechanisms than in their unicellular counterparts. 9,10 In order to gain more insight into SAGA function in multicellular eukaryotes, we turned to Drosophila.…”

Section: 2mentioning

confidence: 99%