TFIIB and subunits of the SAGA complex are involved in transcriptional activation of phospholipid biosynthetic genes by the regulatory protein Ino2 in the yeastSaccharomyces cerevisiae

Abstract

SummaryIn the yeast Saccharomyces cerevisiae , genes involved in phospholipid biosynthesis are activated by ICRE (inositol/choline-responsive element) upstream motifs and the corresponding heterodimeric binding factor, Ino2 + + + + Ino4. Both Ino2 and Ino4 contain basic helix-loop-helix (bHLH) domains required for ICRE binding, whereas transcriptional activation is mediated exclusively by Ino2. In this work, we describe a molecular analysis of functional minimal domains responsible for specific DNA recognition and transcriptional activation (TAD1 and TAD2). We also define the importance of individual amino acids within the more important activation domain TAD1. Random mutagenesis at five amino acid positions showed the importance of acidic as well as hydrophobic residues within this minimal TAD. We also investigated the contribution of known general transcription factors and co-activators for Ino2-dependent gene activation. Although an ada5 single mutant and a gal11 paf1 double mutant were severely affected, a partial reduction in activation was found for gcn5 and srb2 . Ino2 interacts physically with the basal transcription factor Sua7 (TFIIB of yeast). Interestingly, interaction is mediated by the HLH dimerization domain of Ino2 and by two non-overlapping domains within Sua7. Thus, Sua7 may compete with Ino4 for binding to the Ino2 activator, creating the possibility of positive and negative influence of Sua7 on ICREdependent gene expression.

A role for DNA sequence in controlling the spatial organization of the genome

“…48 Acetylation by the catalytic subunit of SAGA, the Gcn5 protein, promotes transcription initiation of the INO1 and GAL1 genes, both of which are targeted to the nuclear periphery upon activation. 49,50 Therefore, localization to the nuclear periphery may help overcome rate-limiting steps in transcription initiation by providing increased access to SAGA components. Though this is an attractive model for the INO1 and GAL1 genes, it does not explain the role of NPC interaction in the transcription of TSA2, a gene not regulated at the level of chromatin.…”

Mediator subunits and histone methyltransferase Set2 contribute to Ino2-dependent transcriptional activation of phospholipid biosynthesis in the yeast Saccharomyces cerevisiae

“…Thus, recruitment of histone acetyltransferases (HATs) and deacetylases (HDACs), histon methyltransferases (HMTs) and demethylases (HDMs) essentially aVects the access of the transcriptional machinery to promoter regions. We and others have previously shown that the HAT complex SAGA contributes to Ino2-dependent gene activation (Dietz et al 2003;Lo et al 2005). However, SAGA is not recruited directly but instead requires phosphorylation of histone H3 at Ser10 by the histone kinase Snf1 which is bound by Ino2.…”

“…While Ino4 is required for ICRE binding and nuclear import of the complex, transcriptional activation is mediated exclusively by Ino2 containing two separate activation domains (Schwank et al 1995;Dietz et al 2003;Kumme et al 2008). Activation of target genes occurs when the supply of phospholipid precursors inositol and choline is limiting, leading to an excess of phosphatidic acid (PA) which prevents nuclear localization of repressor Opi1 (Loewen et al 2004; reviewed by Chen et al 2007).…”

“…We have previously shown that Ino2 directly contacts Sua7 (TFIIB in yeast) via its helix-loop-helix domain (Dietz et al 2003). Although growth of a snf1 mutant is severely retarded in the absence of inositol, a considerable degree of Ino2-dependent transcription remains.…”

Rapid hyperosmotic coinduction of two tilapia ( Oreochromis mossambicus ) transcription factors in gill cells

“…One class is preferentially targeted by the Spt-Ada-GCN5-acetyltransferase (SAGA) transcriptional complex and contains many stress-inducible genes (Ϸ10% of the genome), whereas the other class is preferentially targeted by the TFIID transcriptional complex and associated with house-keeping functions (Ϸ90% of the genome). TFIIB cooperates with the yeast SAGA complex (25), and it is possible that similar interactions direct TFIIB function during osmotic stress in vertebrates.…”