4L81:
reference: Structural basis for diversity in the SAM clan of riboswitches., Trausch JJ, Xu Z, Edwards AL, Reyes FE, Ross PE, Knight R, Batey RT, Proc Natl Acad Sci U S A. 2014 May 6;111(18):6624-9. doi:, 10.1073/pnas.1312918111. Epub 2014 Apr 21. PMID: 24753586

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