Comparison of the PSG family members in human, baboon, mouse, and rat show some conserved elements. For example, an arginine at position 64 and an aspartic acid at position 82 are believed to form a salt bridge [18] . Between the amino acids forming the putative salt bridge are two (out of a total of three) potential N-linked glycosylation sites in the N-domain of all human PSGs. These potential N-linked glycosylation sites are also conserved in all mouse PSGs and in the majority of baboon and rat PSGs. Because the importance of N-linked glycosylation and the putative salt bridge has never been explored, we introduced three mutations that render a protein without the conserved N-linked glycosylation sites and the ability to form the salt bridge. As expected, this protein has a lower molecular weight than wild-type PSG1 (Fig. 7A, lane 3) . The PSG1RNN!AAA mutant did not induce TGFB1 in any of the cells tested, as shown in Figure 7B for HTR-8/SVneo cells.