Expression of human GlcNAc-phosphotransferase γ subunit in COS cells. Membrane fractions of COS cells transfected with either the epitope-tagged γ-subunit cDNA or a vector control were analyzed by immunoblot. The samples were analyzed by 7.5% SDS-PAGE under reducing and nonreducing conditions followed by transfer to a nitrocellulose membrane, which was probed with mAb HPC4 and ¹²⁵I-labeled goat anti-mouse IgG. Disulfide bonds were reduced with 10% β-mercaptoethanol in samples electrophoresed in lanes labeled +SH. The migration positions of molecular mass markers (in kDa) are indicated on the left.