SummaryIn the yeastSaccharomyces cerevisiae, genes involved in phospholipid biosynthesis are activated by ICRE (inositol/choline‐responsive element) up‐stream 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 anada5single mutant and agal11 paf1double mutant were severely affected, a partial reduction in activation was found forgcn5andsrb2. 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 ICRE‐dependent gene expression.

Dietz, M., Heyken, W., Hoppen, J., Geburtig, S., & Schüller, H. (2003). 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. Molecular Microbiology, 48(4), 1119–1130. Portico.