Has guanine nucleotide-binding activity but lacks intrinsic GTPase activity. Probably required for the amino acid- induced 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. Forms a heterodimer with RRAGA in a sequence-independent manner. Binds GTP. Interacts with NOL8 and RRAGB. Belongs to the GTR/RAG GTP-binding protein family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.