Infection by ecotropic MLV, including the Friend MLV, is mediated by the binding of the viral Env protein to the rodent ortholog of cationic amino acid transporter 1 (CAT-1), which serves as the specific cellular receptor (Albritton et al., 1989; Kim et al., 1991; Wang et al., 1991). The gene discussed is SLC7A1; the disease is infection.