RRAGC (Ras-related GTP-binding protein C) is a guanine nucleotide-binding protein that serves as a critical regulator of mTORC1 signaling in response to amino acid availability 12. RRAGC functions as part of a heterodimeric Rag complex with RagA or RagB, where it cycles between inactive (GTP-bound) and active (GDP-bound) conformational states 23. In its GDP-bound active form, RRAGC recruits mTORC1 to lysosomes for activation by RHEB, enabling canonical amino acid-stimulated mTORC1 signaling 12. Beyond canonical mTORC1 activation, RRAGC mediates a substrate-specific pathway controlling phosphorylation of transcription factors TFEB and TFE3, master regulators of lysosomal biogenesis and autophagy, independent of RHEB activity 45. The Rag-Ragulator complex, organized around RRAGC, serves as the central physical architecture organizing nutrient-sensing components on the lysosomal surface 6. Disease-causing de novo missense variants in RRAGC cause constitutive mTORC1 hyperactivation, resulting in early-onset mTORopathy with dilated cardiomyopathy, hepatopathy, and neurological abnormalities including pachygyria and polymicrogyria 7. Additionally, RRAGC activity is disrupted during proteotoxic stress to activate TFEB-mediated autophagy through non-canonical mechanisms 8. These findings establish RRAGC as a central hub integrating nutrient and stress signals to coordinate mTORC1-dependent cell growth with lysosomal function.