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Bradfield JY, Lee YH, Keeley LL.Bradfield JY, et al. Among authors: keeley ll.Proc Natl Acad Sci U S A. 1991 May 15;88(10):4558-62. doi: 10.1073/pnas.88.10.4558.Proc Natl Acad Sci U S A. 1991.PMID: 2034694Free PMC article.