Transmembrane (TM) (345 amino acids)

TM is also known as gp41 and as stated above comes from the env protein, gp160. This is the fusogen proteins, that is it mediates the fusion of the viral membrane and the cell membrane after the virus has bound to the receptors. It has a N-terminal hydrophobic region that is rich in glycine. The transmembrane region is also hydrophobic and involved in fusion. The core region of TM forms a trimer of alpha helices (thus the TM/SU complexes also form trimers)

For further information see: Alan Frankel and John A. T. Young, HIV-1: Fifteen proteins and an RNA Annual Review of Biochemistry 67: 1-25, 1998