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Figure 7
2mFo − DFc map of the Sm-site region superimposed on the re-refined structure. The electron-density map is averaged over the 12 NCS copies after sharpening in REFMAC5 (B = −16.38 Å2 for simple map sharpening; B = −61.47Å2, α = 0.0235 for regularized map sharpening) and contoured at 0.54 e Å−3. The superposition shows that each base of the U4 Sm-site heptad (118-AAUUUUU-124) is bound in one Sm protein. The white arrow in the central hole points to the density feature at the equivalent location to a hydrated Mg2+ ion in the U1 Sm site. The black arrow at the lower right points to the solvent-exposed N6 atom of A118. |
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