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Qin S, Zhou HX.Qin S, et al.Proc Natl Acad Sci U S A. 2009 Apr 28;106(17):6974-9. doi: 10.1073/pnas.0900291106. Epub 2009 Apr 3.Proc Natl Acad Sci U S A. 2009.PMID: 19346475Free PMC article.