A fast selenium derivatization strategy for crystallization and phasing of RNA structures

Detailed views of the labeled U2650·A2670 (A, C) and of the labeled U2656·A2665 reverse wobble (B, D) base-pairs in SRL structures. (A, B) The 2Fo-Fc electron density map at 0.97 Å and 0.96 Å resolution are represented around the refined model. (C) The experimental SAD electron density map at 1.1 Å resolution is shown around the U2650-SeCH₃ A2670. (D) The experimental MAD electron density map at 1.0 Å resolution, as well as the anomalous map contoured at 40 σ level (in green), is shown for the U2656-SeCH₃ SRL structure. Spheres of electron density around RNA correspond to water molecules. Hydrogen bonds and the intra-residue C-H(methyl)-O bond in modified uridines are represented with black and gray dotted lines, respectively.