GlcNAcT-I-KDEL localized mainly in the ER is active. Lec1 cells stably expressing empty vector, GlcNAcT-I-HA-KDEL, or GlcNAcT-I-HA were analyzed for (A) Con A resistance and (B) L-PHA-FITC binding by flow cytometry. (C) GlcNAcT-I and β4GalT activities in transfectant lysates were determined. Bars represent range (n = 2). (D) HeLa cells transiently expressing GlcNAcT-I-HA-KDEL were fixed and immunofluorescently labeled for GlcNAcT-I-HA-KDEL (red) and endogenous ManII (green). Bars, 10 µm.