The mechanistic target of rapamycin complex 1 (mTORC1) coordinates cell growth with its nutritional, hormonal, energy, and stress status. Amino acids are critical regulators of mTORC1 that permit other inputs to mTORC1 activity. However, the roles of individual amino acids and their interactions in mTORC1 activation are not well understood. Here we demonstrate that activation of mTORC1 by amino acids includes two discrete and separable steps: priming and activation. Sensitizing mTORC1 activation by priming amino acids is a prerequisite for subsequent stimulation of mTORC1 by activating amino acids. Priming is achieved by a group of amino acids that includes L-asparagine, L-glutamine, L-threonine, L-arginine, L-glycine, L-proline, L-serine, L-alanine, and L-glutamic acid. The group of activating amino acids is dominated by L-leucine but also includes L-methionine, L-isoleucine, and L-valine. L-Cysteine predominantly inhibits priming but not the activating step. Priming and activating steps differ in their requirements for amino acid concentration and duration of treatment. Priming and activating amino acids use mechanisms that are distinct both from each other and from growth factor signaling. Neither step requires intact tuberous sclerosis complex of proteins to activate mTORC1. Concerted action of priming and activating amino acids is required to localize mTORC1 to lysosomes and achieve its activation.

In the originally published Fig. 1A, the immunoblots for total S6K were an inadvertent copy of the S6K immunoblots in Fig. 2A. The mistake was caused by confusion over file names during creation of the figure. This error has now been corrected. The bar graphs in the original Fig. 1, B and C, are based on quantitation of multiple blots and are correct as shown. This correction does not affect the results or conclusions of this work.