Fig. 1.

(A) Secondary structure of the HIV-1 5′-L₃₅₆ in its DIS-exposed, dimer-promoting state (adapted from ref. 57; residues truncated in 5′-L₃₄₄ colored gray). The 5′-L₃₄₄ NMR signals with resolved and assigned 2D ¹H–¹H NOESY cross-peaks are denoted by color shaded boxes; yellow denotes sites that were only assignable in mutant constructs that either lacked the upper PBS loop (5′-L_344ΔPBS) (57) or contained an lrAID substitution in the U5:AUG stem (5′-L_344-UUA) (48). Intact (B) and truncated (C) 5′-leader constructs rapidly dimerize when incubated in PI buffer at 37 °C. Dimerization profiles on TB and TBM gels are indistinguishable, indicating that the dimers are nonlabile. o/n, overnight. (D) Region of the 2D ¹H–¹H NOESY spectrum of A^2rG^rC^r-labeled 5′-L₃₄₄ RNA. Assignments (adenosine-H2 and ribose-H₁′ assignments labeled vertically and horizontally, respectively) are color-coded to match the highlighted elements within the secondary structure in A.