Guanine nucleotide-binding protein that plays a crucial role in the cellular response to amino acid availability through regulation of the mTORC1 signaling cascade (PubMed:20381137, PubMed:24095279, PubMed:25936802, PubMed:31601708, PubMed:31601764, PubMed:38103557). Forms heterodimeric Rag complexes with RagC/RRAGC or RagD/RRAGD and cycles between an inactive GDP-bound and an active GTP-bound form: RagA/RRAGA is in its active form when GTP-bound RagA/RRAGA forms a complex with GDP-bound RagC/RRAGC (or RagD/RRAGD) and in an inactive form when GDP-bound RagA/RRAGA heterodimerizes with GTP-bound RagC/RRAGC (or RagD/RRAGD) (PubMed:20381137, PubMed:24095279, PubMed:25936802, PubMed:31601708, PubMed:31601764, PubMed:32868926). In its GTP-bound active form, promotes the recruitment of mTORC1 to the lysosomes and its subsequent activation by the GTPase RHEB (PubMed:20381137, PubMed:25936802, PubMed:31601708, PubMed:31601764). Involved in the RCC1/Ran-GTPase pathway (PubMed:9394008). May play a direct role in a TNF signaling pathway leading to induction of cell death (PubMed:8995684). {ECO:0000269|PubMed:20381137, ECO:0000269|PubMed:24095279, ECO:0000269|PubMed:25936802, ECO:0000269|PubMed:31601708, ECO:0000269|PubMed:31601764, ECO:0000269|PubMed:32868926, ECO:0000269|PubMed:38103557, ECO:0000269|PubMed:8995684, ECO:0000269|PubMed:9394008}. (Microbial infection) May alternatively act as a cellular target for adenovirus E3-14.7K, an inhibitor of TNF functions, thereby affecting cell death. . This is the function of RRAGA (Ras related GTP binding A, Ensembl gene identifier ENSG00000155876).