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Singh R, Xu J, Berger B.Singh R, et al. Among authors: xu j.Proc Natl Acad Sci U S A. 2008 Sep 2;105(35):12763-8. doi: 10.1073/pnas.0806627105. Epub 2008 Aug 25.Proc Natl Acad Sci U S A. 2008.PMID: 18725631Free PMC article.