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Shapiro ML, Ferbinteanu J.Shapiro ML, et al.Proc Natl Acad Sci U S A. 2006 Mar 14;103(11):4287-92. doi: 10.1073/pnas.0508688103. Epub 2006 Mar 3.Proc Natl Acad Sci U S A. 2006.PMID: 16537523Free PMC article.