Gap junction beta-1 protein (GJB1), also known as connexin 32 (Cx32), is a transmembrane protein that in humans is encoded by the GJB1 gene. Gap junction beta-1 protein is a member of the gap junction connexin family of proteins that regulates and controls the transfer of communication signals across cell membranes, primarily in the liver and peripheral nervous system. Connexins are membrane-spanning proteins that assemble to form gap junction channels that facilitate the transfer of ions and small molecules between cells. For a general discussion of connexin proteins, see GJB2. In Schwann cells, GJB1 also forms channels that facilitate transfers between layers of the myelin. In melanocytic cells GJB1 gene expression may be regulated by MITF.