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Xie, Sancai, Jonathan Green, James B. Bixby, Bozena Szafranska, James C. DeMartini, Steven Hecht, a R. Michael Roberts. "The Diversity and Evolutionary Relationships of the Pregnancy-associated Glycoproteins, an Aspartic Proteinase Subfamily Consisting of Many Trophoblast-expressed genes." Proc Natl Acad Sci U S A 1997.

Xie, Sancai, et al. "The Diversity and Evolutionary Relationships of the Pregnancy-associated Glycoproteins, an Aspartic Proteinase Subfamily Consisting of Many Trophoblast-expressed genes." Proc Natl Acad Sci U S A 1997.