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Levine MT, Jones CD, Kern AD, Lindfors HA, Begun DJ.Levine MT, et al.Proc Natl Acad Sci U S A. 2006 Jun 27;103(26):9935-9. doi: 10.1073/pnas.0509809103. Epub 2006 Jun 15.Proc Natl Acad Sci U S A. 2006.PMID: 16777968Free PMC article.