Coordinate regulation of multiple and distinct biosynthetic pathways by TOR and PKA kinases in S. cerevisiae.

The target of rapamycin (TOR) signaling pathway is an essential regulator of cell growth in eukaryotic cells. In Saccharomyces cerevisiae, TOR controls the expression of many genes involved in a wide array of distinct nutrient-responsive metabolic pathways. By exploring the TOR pathway under different growth conditions, we have identified novel TOR-regulated genes, including genes required for branched-chain amino acid biosynthesis as well as lysine biosynthesis (LYS genes). We show that TOR-dependent control of LYS gene expression occurs independently from previously identified LYS gene regulators and is instead coupled to cAMP-regulated protein kinase A (PKA). Additional genome-wide expression analyses reveal that TOR and PKA coregulate LYS gene expression in a pattern that is remarkably similar to genes within the ribosomal protein and "Ribi" regulon genes required for ribosome biogenesis. Moreover, this pattern of coregulation is distinct from other clusters of TOR/PKA coregulated genes, which includes genes involved in fermentation as well as aerobic respiration, suggesting that control of gene expression by TOR and PKA involves multiple modes of crosstalk. Our results underscore how multiple signaling pathways, general growth conditions, as well as the availability of specific nutrients contribute to the maintenance of appropriate patterns of gene activity in yeast.