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Shimkets L, Woese CR.Shimkets L, et al.Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9459-63. doi: 10.1073/pnas.89.20.9459.Proc Natl Acad Sci U S A. 1992.PMID: 1384053Free PMC article.