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Roop DR, Hawley-Nelson P, Cheng CK, Yuspa SH.Roop DR, et al. Among authors: yuspa sh.Proc Natl Acad Sci U S A. 1983 Feb;80(3):716-20. doi: 10.1073/pnas.80.3.716.Proc Natl Acad Sci U S A. 1983.PMID: 6187003Free PMC article.