Fusion of HIV with target cell plasma membranes is mediated largely by the gp41 glycoprotein. This glycoprotein contains a stretch of strongly hydrophobic amino acids flanked by a series of polar amino acids at its N terminus. Subsequent to the second conformation change in gp120, the N-terminal fusion peptide of gp41 adopts a position which brings it into close proximity with the target cell plasma membrane. As gp41 is found in trimers within the viral membrane, the resulting structure of this conformational change is often referred to as a “prong”, in which three N-terminal peptides extend towards the target cell plasma membrane. The process of fusion begins at this time, with the N-terminus of gp41 inserting itself into the membrane of the target cell.