Gcn5 is required for several common stress responses in divergent yeast species and defects in its conserved histone acetyltransferase domain cause stress sensitivity. (A) Gcn5 is required for efficient growth under a common set of environmental stress conditions in evolutionarily divergent yeast species. The figure shows serial dilutions of wild type (wt) or mutant (gcn5Δ) yeast cells spotted on normal growth media (control) or media containing stress inducing levels of KCl, CaCl2, Calcoflour White, MnCl2 and caffeine. (B) The domain structure of Gcn5 showing the highly conserved histone acetyltransferase (HAT). The diagram shows the HAT, the Ada2-interaction domain (ADA2) and the Bromo domain (Bromo) domains defined previously for the S. cerevisiae protein . Residue numbers equivalent to domain boundaries are shown. The extent of domain identity between S. cerevisiae and S. pombe is shown (%). The approximate position of each mutant triple-alanine substitution mutant, starting at residues 126, 129 and 132 respectively, is shown. (C) The HAT activity of Gcn5 is required for Gcn5 dependent stress responses. Cell plating assay performed as in Fig. 1A showing S. cerevisiae gcn5Δ cells carrying pRS316 plasmids expressing either wild type GCN5 or GCN5 with substitution mutations in the HAT domain as indicated in (B). Wild type (wt) and GCN5- (gcn5Δ) cells were used as controls.