Scratchboard drawing of ribonuclease S (ribonuclease A cleaved by subtilisin between residues 20 and 21, but still folded).  Crystal structure by H. W. Wyckoff &amp; F. M. Richards in 1967.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1">[1]</a></sup>  Image hand-drawn by Jane S. Richardson in 1980 as the frontispiece to Anatomy and Taxonomy of Protein Structures.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2">[2]</a></sup><ol class="references"><li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text"><cite style="font-style:normal">Wyckoff HW, Hardman KD, Allewell NM, Inagami T, Johnson LN, Richards FM (1967). "The structure of ribonuclease-S at 3.5 Å resolution". <i>J Biol Chem</i> <b>242</b>: 3984-3988.</cite></span>
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<li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text"><cite style="font-style:normal">Richardson JS (1981). "The Anatomy and Taxonomy of Protein Structures". <i>Adv Protein Chem</i> <b>34</b>: 167-339. <a href="https://en.wikipedia.org/wiki/Digital_object_identifier" class="extiw" title="w:Digital object identifier">DOI</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1016/S0065-3233(08)60520-3">10.1016/S0065-3233(08)60520-3</a>.</cite></span>
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