Studying the structures of 2×2 GG/GG internal loops by NMR spectroscopy. To verify the computational predictions, the RNA construct, r(CCAGGGCAAGGAAACUUGGGCUGG), was designed to eliminate potential strand slippage as observed previously . When folded, this construct includes a 2×2 GG/GG internal loop as well as a stable GNRA tetraloop of GAAA, a site-specific G/C to A/U modification adjacent to the closing pairs of the internal loop, and two capping GC base pairs (Figure ). Preliminary 1 H 2D NMR characterization of exchangeable protons revealed a well-formed GNRA tetraloop, with an off-diagonal peak at ~10.5 ppm corresponding to stacking between the GNRA and upper helix 66 (Figure ). The canonical base pairs of the upper and lower helix are well formed, with sharp peaks in the 12.5-14.0 ppm range.