7KCI:
reference: Determinants of repressor/operator recognition from the structure of the trp operator binding site., Shakked Z, Guzikevich-Guerstein G, Frolow F, Rabinovich D, Joachimiak A, Sigler PB, Nature. 1994 Mar 31;368(6470):469-73. doi: 10.1038/368469a0. PMID: 8133895

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