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Nenninger AA, Robinson LS, Hultgren SJ.Nenninger AA, et al. Among authors: robinson ls.Proc Natl Acad Sci U S A. 2009 Jan 20;106(3):900-5. doi: 10.1073/pnas.0812143106. Epub 2009 Jan 8.Proc Natl Acad Sci U S A. 2009.PMID: 19131513Free PMC article.