An example of diagnosing a problem region of RNA backbone conformation in a crystal-structure model, and a rebuilding step that fixes the problem.  The cluster of hotpink spikes marks an impossible all-atom steric overlap, and the green lines and "!!" label mark an unrecognized conformation of the backbone torsion angles.  Refitting into one of the recognized backbone conformers also corrects the steric clash and creates a good hydrogen bond (green dots).  Residue 77 in the S-motif of the 5S RNA of PDB file 3cc2, diagnosed in MolProbity and rebuilt in KiNG.
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