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Gao X, Tate P, Hu P, Tjian R, Skarnes WC, Wang Z.Gao X, et al.Proc Natl Acad Sci U S A. 2008 May 6;105(18):6656-61. doi: 10.1073/pnas.0801802105. Epub 2008 Apr 30.Proc Natl Acad Sci U S A. 2008.PMID: 18448678Free PMC article.