RVs use their envelope proteins to bind a variety of receptor molecules such as murine cationic amino acid transporter (mCAT), a sodium-dependent Pi transporter (PiT2), xenotropic and polytropic retrovirus receptor 1 (XPR1), CD4, CD46, CD150, and the RD114-and-D-type-retrovirus/alanine-serine-cysteine transporter 2 (RDR/ASCT2) expressed on different cell surfaces to initiate infection, a critical step in determining the target cell tropism of the virus. The gene discussed is SLC1A5; the disease is infection.