Susceptibility to murine ecotropic retroviruses is attributed to the binding of the virus envelope to the membrane receptor encoded by the Rec1 gene. HCAT1 was identified as the principal transporter of the cationic amino acids, arginine, lysine, and ornithine in mouse cells. the Rec1 gene mapped to mouse chromosome 5 by analysis of murine-hamster somatic cell hybrids. Using a human cDNA obtained by homology to Rec1, Albritton et al. (1992) determined the location of the human cationic amino acid transporter by somatic cell genetics, in situ hybridization, and RFLP linkage analysis. The studies indicated that ATRC1 is located at 13q12-q14, closely linked to ATP1AL1. The CEPH consortium linkage map of chromosome 13 published by Bowcock et al. (1993) showed ATRC1 to be distal to ATP1AL1.