Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
The "env" gene in HIV encodes a single protein, gp160. (When gp160 is synthesised in the cell, cellular enzymes add complex carbohydrates and turn it from a protein into a glycoprotein - hence the name "gp160" rather than "p160".)
gp160 travels to the cell surface, where cellular enzymes again attack it, this time chopping into two pieces - gp120, and gp41. If and when new virus particles bud off from the host cell, these two pieces lie on opposite sides of the virus membrane. gp120 sits on the outside of the virus particle, forming the virus's spikes, while gp41 sits just on the inside of the membrane - each gp41 being anchored to a gp120 through the membrane.
How many spikes does a HIV particle have? It's a tricky question, but the answer seems likely to be about 9 or 10. This is a lot fewer spikes than you'll see on most diagrams of HIV! There's a bit of confusion since some studies have decided that HIV particles normally have 72 spikes, whilst some other studies have decided that they have normally no more than ten. It's hard to say for certain who's right....