Figure 2.

U-U mismatch geometries in the crystal structures. Three different states of U–U mismatch geometries are observed in the A, M3 and B, M2 RNA crystal structures. The MM1 and MM2 states showed inclined asymmetric mismatch pair formation stabilized by one direct hydrogen-bonded interaction. In the MMT state, the central U–U mismatch pair does not show any direct H-bonded interaction while the central A–U base pair is stabilized by two hydrogen-bonded interactions. Water molecules (red spheres) bridging U–U mismatches in the major and minor grooves are shown with the refined 2mF_o–DF_c maximum likelihood-weighted Fourier electron density map countered at the 1.0 σ level. The values for inclination angles (λ angle) and C1′–C1′ distances are given below each mismatch type.