4E2T:
reference: NMR and Crystal Structures of the Pyrococcus horikoshii RadA Intein Guide a Strategy for Engineering a Highly Efficient and Promiscuous Intein., Oeemig JS, Zhou D, Kajander T, Wlodawer A, Iwai H, J Mol Biol. 2012 Aug 3;421(1):85-99. Epub 2012 May 2. PMID: 22560994

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