The S. pombe SAGA complex controls the switch from proliferation to sexual differentiation through the opposing roles of its subunits Gcn5 and Spt8

Abstract

The SAGA complex is a conserved multifunctional coactivator known to play broad roles in eukaryotic transcription. To gain new insights into its functions, we performed biochemical and genetic analyses of SAGA in the fission yeast, Schizosaccharomyces pombe. Purification of the S. pombe SAGA complex showed that its subunit composition is identical to that of Saccharomyces cerevisiae. Analysis of S. pombe SAGA mutants revealed that SAGA has two opposing roles regulating sexual differentiation. First, in nutrient-rich conditions, the SAGA histone acetyltransferase Gcn5 represses ste11 + , which encodes the master regulator of the mating pathway. In contrast, the SAGA subunit Spt8 is required for the induction of ste11 + upon nutrient starvation. Chromatin immunoprecipitation experiments suggest that these regulatory effects are direct, as SAGA is physically associated with the ste11 + promoter independent of nutrient levels. Genetic tests suggest that nutrient levels do cause a switch in SAGA function, as spt8⌬ suppresses gcn5⌬ with respect to ste11 + derepression in rich medium, whereas the opposite relationship, gcn5⌬ suppression of spt8⌬, occurs during starvation. Thus, SAGA plays distinct roles in the control of the switch from proliferation to differentiation in S. pombe through the dynamic and opposing activities of Gcn5 and Spt8.[Keywords: S. pombe; transcription; differentiation; SAGA; Gcn5; Ste11] Supplemental material is available at http://www.genesdev.org.

Transcriptional Regulation inSaccharomyces cerevisiae: Transcription Factor Regulation and Function, Mechanisms of Initiation, and Roles of Activators and Coactivators

“…For example, genome-wide characterization of Gcn5-responsive genes reveals that Gcn5 functions as both a coactivator and a corepressor in S. cerevisiae and Schizosaccaromyces pombe (Xue-Franzen et al 2010). Gene expression studies have also shown that Gcn5 and subunits of the SAGA TBP-binding module have opposing roles; S. cerevisiae SPT3 and GCN5 mutations were found to have opposite effects in transcriptional regulation of the HO and STE11 genes (Yu et al 2003;Helmlinger et al 2008), although it is possible that some of these phenotypes are due to indirect effects. SAGA can also repress basal expression of some genes in vitro and in vivo (Belotserkovskaya et al 2000;Warfield et al 2004).…”

“…These mutations are presumably altered in their interaction with TBP because several can be suppressed in an allele-specific fashion by mutations in TBP. However, the interaction of SAGA and TBP is complex because mutations in Spt3 and Spt8 can have both positive and negative effects on gene expression (Yu et al 2003;Helmlinger et al 2008). Both Spt3 and Spt8 crosslink to TBP in PICs (Mohibullah and Hahn 2008), and mutations in Spt3 and Spt8 show defects in TBP recruitment in vivo (Dudley et al 1999;Larschan and Winston 2001;Bhaumik and Green 2002;Barbaric et al 2003;Mohibullah and Hahn 2008).…”

The SAGA Histone Acetyltransferase Complex Regulates Leucine Uptake through the Agp3 Permease in Fission Yeast

“…In fission yeast, the SAGA complex consists of 19 subunits, all of which are conserved in budding yeast (13). SAGA contains the histone acetyltransferase (HAT) catalytic subunit, Gcn5 (12,14).…”

“…SAGA contains the histone acetyltransferase (HAT) catalytic subunit, Gcn5 (12,14). Deletion of gcn5 ϩ in fission yeast results in a global decrease in acetylation of histone H3 residues Lys-9, Lys-14, and Lys-18, but changes the expressions of only a relatively small subset of genes (1-2%) by more than 2-fold (13,15). SAGA is known to control sexual differentiation in S. pombe (13).…”

“…Deletion of gcn5 ϩ in fission yeast results in a global decrease in acetylation of histone H3 residues Lys-9, Lys-14, and Lys-18, but changes the expressions of only a relatively small subset of genes (1-2%) by more than 2-fold (13,15). SAGA is known to control sexual differentiation in S. pombe (13). The gcn5⌬ fission yeast also exhibits sensitivities to high temperature and high concentrations of KCl (15,16).…”