Figure 3. Structural model of HIV-1 Rev bound to RRE stem-loop IIB. The amino-terminal half of Rev is depicted bound to its high-affinity RNA ligand. The RNA stem-loop (gold) makes direct contact with an arginine-rich alpha-helix of Rev (violet). Only those protein sidechains that constitute the two surfaces of Rev critical for multimeric assembly are shown (tail surface, red; head surface, blue).