Guanine nucleotide-binding protein that plays a crucial role in the cellular response to amino acid availability through regulation of the mTORC1 signaling cascade. Forms heterodimeric Rag complexes with RRAGA or RRAGB and cycles between an inactive GTP-bound and an active GDP-bound form. In its active form participates in the relocalization of mTORC1 to the lysosomes and its subsequent activation by the GTPase RHEB. This is a crucial step in the activation of the TOR signaling cascade by amino acids. GTP + H2O = GDP + H(+) + phosphate In high-amino acid conditions, activated by GTPase activating protein (GAP) FLCN that stimulates RRAGC GTPase activity to turn it into its active GDP-bound form. Forms a heterodimer with RRAGA, in a sequence-independent manner, and RRAGB (By similarity). Heterodimerization stabilizes proteins of the heterodimer (By similarity). In complex with RRAGA or RRAGB, interacts with RPTOR; this interaction is particularly efficient with GTP-loaded RRAGB and GDP-loaded RRAGC (By similarity). Component of the lysosomal folliculin complex (LFC), composed of FLCN, FNIP1 (or FNIP2), RRAGA/RagA or RRAGB/RagB GDP-bound, RRAGC/RagC or RRAGD/RagD GTP-bound, and Ragulator (By similarity). Interacts with NOL8 (By similarity). Interacts with SH3BP4; the interaction with this negative regulator is most probably direct, preferentially occurs with the inactive GDP-bound form of RRAGB, is negatively regulated by amino acids and prevents interaction with RPTOR (By similarity). The Rag heterodimer interacts with SLC38A9; the probable amino acid sensor (By similarity). Interacts with SESN1, SESN2 and SESN3 (PubMed:25259925). Interacts with PIP4P1 (PubMed:29644770). The GDP-bound form interacts with TFE3 (PubMed:30595499). Predominantly cytoplasmic. May shuttle between the cytoplasm and nucleus, depending on the bound nucleotide state of associated RRAGA. Expressed most abundantly in kidney. Moderately expressed in brain, ovary, and testis, and detected at lower levels in heart, liver, and muscle. Not detected in lung, spleen, and small intestine. Widely expressed in tumor cells, with expression being specifically up-regulated in highly metastatic cells. Belongs to the GTR/RAG GTP-binding protein family.