1U9I:
reference: Identification of key phosphorylation sites in the circadian clock protein KaiC by crystallographic and mutagenetic analyses., Xu Y, Mori T, Pattanayek R, Pattanayek S, Egli M, Johnson CH, Proc Natl Acad Sci U S A 2004 Sep 21;101(38):13933-8. Epub 2004 Sep 3. PMID: 15347809

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