Figure 1.

TOR Evolved an Early Role to Coordinate Ribosome Biogenesis with Metabolic Status in Eukaryotes

TOR complex 1 (TORC1) is an atypical protein kinase that evolved in the last common ancestor of present-day eukaryotes. TORC1 integrates diverse upstream cues to coordinate cellular metabolism, broadly promoting anabolism when growth can be supported by available nutrients and environmental conditions. There is considerable variation in the upstream regulators and downstream effectors of TOR signaling across eukaryotic lineages, but consistently, TOR senses the levels of monomeric constituents of ribosomes (amino acids and nucleotides) and energy stores to stimulate ribosome biogenesis and growth.