Fig. 4.

Balancing amino-acid supply and demand in familiar and novel conditions. a Expression of amino-acid biosynthesis genes vs. RP genes for various environmental conditions including temperature and osmotic shock, amino-acid starvation, nitrogen depletion, addition of hydrogen-peroxide/menadione/DTT (light gray, Gasch et al.), a set of gene deletion mutant strains (Hughes et al., dark gray), the twelve wild type strains used in this work (green) and the twelve evolved strains (yellow). Red arrow indicates the vector of change during evolution. b Model for amino-acid supply and demand balance. In a familiar environment, amino-acid supply and demand are balanced by evolutionarily tuned adjustment of ribosome abundance. In novel conditions un-optimized by evolution, a shortage in amino-acid results in accumulation of uncharged tRNAs, which acts as an internal signal for GCN4-mediated induction of amino-acid biosynthesis genes