SAMTOR (S-adenosylmethionine sensor upstream of mTORC1) is a SAM-binding protein that acts as a nutrient sensor linking methionine metabolism to mTORC1 signaling. SAMTOR inhibits mTORC1 by interacting with GATOR1 and KICSTOR complexes; this interaction is disrupted when SAMTOR binds S-adenosylmethionine (SAM) with a dissociation constant of approximately 7 μM 1. Under methionine-replete conditions, SAM binding to SAMTOR causes release from GATOR1/KICSTOR, promoting mTORC1 activation and cell growth 1. Conversely, methionine starvation reduces SAM levels below the dissociation threshold, allowing SAMTOR-GATOR1/KICSTOR reassociation and mTORC1 inhibition 1. Structural studies reveal SAMTOR binds KICSTOR in a manner incompatible with metabolite binding, providing molecular basis for methionine sensing 2. Functionally, SAMTOR participates in the SAMTOR/mTORC1/S6K1/CAD pathway regulating DNA synthesis during embryo implantation 3. SAMTOR has been identified as a characteristic gene in constitutional medicine studies, with diagnostic value in disease detection 4. This SAM-sensing mechanism represents a fundamental link between one-carbon metabolism and mTORC1-mediated growth control.