Conserved cysteine residues in the human immunodeficiency virus type 1 transmembrane envelope protein are essential for precursor envelope cleavage

The transmembrane (TM) protein of human immunodeficiency virus type 1 has been demonstrated to be involved in viral infectivity and syncytium formation. Two highly conserved cysteine residues in the extracellular region of the TM protein are shown to be essential for processing the 160-kDa envelope precursor into the active 120- and 41-kDa mature forms.