The Ragulator complex is a lysosome associated pentameric complex which acts as a guanyl-nucleotide exchange factor for the Rag GTPases (Rags). It tethers the Rags to the lysosome membrane and interacts with the v-ATPase. In response to amino acid availability, this system jointly acts to regulate the translocation to the lysosomal surface, and thereby the activation, of TORC1. (Adapted from FBrf0225443 and FBrf0214985.)