Spt-Ada-Gcn5 acetyltransferase (SAGA) complex is a multicomponent regulator of acetylation.Canzonetta, C., Vernarecci, S., Iuliani, M., Marracino, C., Belloni, C., Ballario, P., & Filetici, P. (2016). SAGA DUB-Ubp8 Deubiquitylates Centromeric Histone Variant Cse4. G3: Genes|Genomes|Genetics, 6(2), 287–298. http://doi.org/10.1534/g3.115.024877 It has been found that this complex is highly conserved between different organisms, such as humans, Drosophila, and yeast. This 15 subunit complex has been best characterized for its histone acetyltransferase activity (HAT).Köhler, A., Zimmerman, E., Schneider, M., Hurt, E., & Zheng, N. (2010). Structural Basis for Assembly and Activation of the Hetero-tetrameric SAGA Histone H2B Deubiquitinase Module. Cell, 141(4), 606–617. http://doi.org/10.1016/j.cell.2010.04.026 The acetylating activity has been found to occur in the lysine residues of the N-terminal tails of H3 and H2 histones.Henry, K. W., Wyce, A., Lo, W.-S., Duggan, L. J., Emre, N. C. T., Kao, C.-F., … Berger, S. L. (2003). Transcriptional activation via sequential histone H2B ubiquitylation and deubiquitylation, mediated by SAGA-associated Ubp8. Genes & Development, 17(21), 2648–2663. http://doi.org/10.1101/gad.1144003 It has been found recently that this activity is actually a deubiquitination of a monoubiquitin that occurs in residue Lys 123 of the H2b histone and the acetylation of the H3 histone. The histone acetylation is mediated by the GCN5 histone acetyl transferase, while the deubiquitinating activity is mediated by a deubiquitinating module (DUBm), which is composed of 4 proteins, Ubp8 ubiquitin hydrolase, Sgf11, Sus1, and Sgf73.Samara, N. L., Datta, A. B., Berndsen, C. E., Zhang, X., Yao, T., Cohen, R. E., & Wolberger, C. (2010). STRUCTURAL INSIGHTS INTO THE ASSEMBLY AND FUNCTION OF THE SAGA DEUBIQUITINATING MODULE. Science, 328(5981), 1025–1029. http://doi.org/10.1126/science.1190049 This DUB module is an independently folding subcomplex that is connected to the C-terminal tail of Sgf 73,Morgan, M. T., Haj-Yahya, M., Ringel, A. E., Bandi, P., Brik, A., & Wolberger, C. (2016). Structural basis for histone H2B deubiquitination by the SAGA DUB module. Science, 351(6274), 725–728. http://doi.org/10.1126/science.aac5681 Sgf73, as well as Sus1, also have a role in facilitating SAGA complex's role in nuclear export by binding to components of the nuclear pore complex. Even though Ubp8 has ubiquitin specific hydrolase (USP) domain, the protein remains inactive unless it is in complex with the other 3 DUBm proteins.
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