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Ryckman BJ, Chase MC, Johnson DC.Ryckman BJ, et al.Proc Natl Acad Sci U S A. 2008 Sep 16;105(37):14118-23. doi: 10.1073/pnas.0804365105. Epub 2008 Sep 3.Proc Natl Acad Sci U S A. 2008.PMID: 18768787Free PMC article.