A137C mutant of gp93 but not natural gp93 dimerizes via a disulfide bond. A, Flow cytometric analysis of the expression of gp93A137C-retroviral transduced mutant pre-B cells by GFP and intracellular Flag staining. B, gp93A137C undergoes disulfide bond-dependent dimerization, whereas WT gp93 does not. gp96Flag, gp93Flag, or gp93A137C-Flag (A137C) were expressed in gp96-deficient pre-B cells, followed by Flag IB in the presence or absence of DTT. Two experiments were done with similar results.