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Iida S, Hiestand-Nauer R, Arber W.Iida S, et al.Proc Natl Acad Sci U S A. 1985 Feb;82(3):839-43. doi: 10.1073/pnas.82.3.839.Proc Natl Acad Sci U S A. 1985.PMID: 2983315Free PMC article.