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Watt KW, Takagi T, Doolittle RF.Watt KW, et al. Among authors: doolittle rf.Proc Natl Acad Sci U S A. 1978 Apr;75(4):1731-5. doi: 10.1073/pnas.75.4.1731.Proc Natl Acad Sci U S A. 1978.PMID: 273904Free PMC article.