Halcyon days of TOR: Reflections on the multiple independent discovery of the yeast and mammalian TOR proteins

The quest to elucidate the molecular mechanism of action of rapamycin in the early 1990s led to the discovery of the novel TOR (target of rapamycin) proteins in yeast and mammalian cells. This was a major breakthrough that resulted in the development of new rapamycin analogs as anti-cancer agents, and launched new research that revealed the pre-eminent biological role of mTOR (mammalian or mechanistic TOR). Beyond mediating rapamycin sensitivity, the TOR proteins are nutrient sensing protein kinases, conserved from yeast to man, with a core function in regulating cell growth, metabolism and overall cell survival. There have been many insightful historical accounts of the origins of TOR; however, the complete TOR dossier would benefit from a chapter on the untold story of the simultaneous co-discovery of the yeast TOR proteins by two independent laboratories, one that is inclusive of the discoveries made at the former SmithKline Beecham (legacy GlaxoSmithKline). Accordingly, this comprehensive retrospective retraces the provenance of yeast TOR (circa 1990-1996) and highlights the early groundbreaking publications that revealed the identity of the TOR genes and proteins. It also commemorates key companion papers which helped to clarify yeast TOR gene nomenclature, identified structural motifs in the predicted TOR protein sequences, demonstrated interactions between yeast FKBP12-rapamycin and TOR, characterized mutations responsible for drug resistance, and began to decipher TOR protein function; some of these crucial early studies appeared in this journal (e.g., Koser et al., 1993. Gene 129, 159-165; Cafferkey et al., 1994. Gene 141, 133-136; Freeman and Livi, 1996. Gene 172, 143-147). A period of intensive investigation, events are portrayed chronologically and juxtaposed alongside the independent parallel efforts to identify and purify mTOR. Finally, in a broader historical context, TOR and mTOR are examined a posteriori as paragons of multiple discovery, illustrating how this common phenomenon (also known as simultaneous invention) can greatly accelerate problem solving and advance human knowledge in a fast-breaking area of scientific research.