The function of ENSG00000239282 (CASTOR1, cytosolic arginine sensor for mTORC1 subunit 1) is as follows. Functions as an intracellular arginine sensor within the amino acid-sensing branch of the TORC1 signaling pathway (PubMed:26972053, PubMed:27487210, PubMed:33594058). As a homodimer or a heterodimer with CASTOR2, binds and inhibits the GATOR subcomplex GATOR2 and thereby mTORC1 (PubMed:26972053, PubMed:27487210, PubMed:33594058). Binding of arginine to CASTOR1 allosterically disrupts the interaction of CASTOR1-containing dimers with GATOR2 which can in turn activate mTORC1 and the TORC1 signaling pathway (PubMed:26972053, PubMed:27487210, PubMed:33594058). {ECO:0000269|PubMed:26972053, ECO:0000269|PubMed:27487210, ECO:0000269|PubMed:33594058}.