Fig. 5.

Mechanism of HIV-1 5′-leader dimerization. (A) In the monomeric conformer, the DIS hairpin is sequestered by intramolecular base pairing with U5 (48). (B) AUG base pairs with U5, displacing the DIS and enabling formation of a labile kissing intermolecular interface, which rapidly transitions to the extended dimer conformer (C). NMR signatures for the kissing species were not observed in the present studies, indicating that it represents a transient species along the dimerization pathway.