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Sharma G, Vijayaraghavan S.Sharma G, et al.Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):4148-53. doi: 10.1073/pnas.071540198. Epub 2001 Mar 20.Proc Natl Acad Sci U S A. 2001.PMID: 11259680Free PMC article.