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Maas RL, Brash AR, Oates JA.Maas RL, et al. Among authors: brash ar.Proc Natl Acad Sci U S A. 1981 Sep;78(9):5523-27. doi: 10.1073/pnas.78.9.5523.Proc Natl Acad Sci U S A. 1981.PMID: 6272308Free PMC article.