FIGURE 5.

Structure determination of the GAAA tetraloop–receptor RNA with associated manganese ions. 2D NOESY data in the absence (A) and the presence (B) of Mn²⁺. (A) 0 μM Mn²⁺, 12 mM MgCl₂. (B) 400 μM Mn²⁺, 12 mM MgCl₂. Boxed regions highlight NOEs involving G9 H8 and A23 H2, shown for comparison. The G9 NOEs are scored as selectively broadened, while the A23 NOEs are not. (C) Superimposition of the 20 lowest-energy structures of the GAAA tetraloop–receptor RNA with associated manganese ions. RNA strands are colored in blue and red, with the backbone highlighted in gray. Manganese ions are shown as green spheres. Five regions of manganese ion association per monomer are numbered.