Basigin (Bsg) is a transmembrane glycoprotein with two immunoglobulin-like domains, and forms a family with embigin and neuroplastin. In these proteins a conserved glutamic acid is present in the middle for the transmembrane domain. Bsg is also called CD147 and EMMPRIN, and the symbol for the human basigin gene is BSG. BSG is located in chromosome 19 band p13. 3. Knockout mice deficient in the Bsg gene are sterile and show various neurological abnormalities. Bsg-deficient embryos are also difficult to implant. Bsg has been found to participate in the cell-surface orientation of monocarboxylic acid transporters (MCTs) to the plasma membrane. Dysfunction of the retina in Bsg-deficient mice is ascribed to the failure of plasma membrane integration of MCTs in the tissue. Bsg is also involved in inflammatory processes and is proposed to be a receptor of cyclophilin A; it is also likely to participate in HIV infection. Bsg in tumor cells triggers the production or release of matrix metalloproteinases in the surrounding mesenchymal cells and tumor cells, thereby contributing to tumor invasion. Furthermore, the association of Bsg with integrins might be important in signaling through Bsg.