The HIV glycoprotein 160 (gp160) is encoded by the env gene and translated to produce a 856-amino acid protein. It forms homotrimers in the host endoplasmic reticulum and is glycosylated the Golgi. It is then cleaved by host furin or furin-like proteases to yield gp41 and gp120, which remain bound non-covalently. gp120 mediates CD4 receptor recognition and gp41 initiates the virus-host membrane fusion. Furin cleavage is ineffecient and can result in producing inactive virions with unprocessed gp160.