Figure 1.

(a) Sequence and secondary structure of HIV-2 TAR. The sequence is identical to HIV-1 TAR except for the deletion of the C24 bulge nucleotide. The nucleotides forming the base triple are shaded in gray. (b) Schematic representation of the HIV-2 TAR base triple formed upon binding argininamide. ^2hJ(N,N) scalar coupled nitrogens forming the reverse Hoogsteen part of the base triple are shown shaded. (c) Observable long range H,N correlations with approximate coupling constant values in cytidine, guanosine, adenosine and uridine, shown as arrows, with the observed non-exchangeable base protons shaded as gray circles.