Figure 4.

GAIP faces the cytoplasm. Membrane fractions (100,000 × g pellet) from AtT-20 cells stably expressing GAIP (clone 14) were treated with proteinase K (+) or buffer alone (−), after which the membranes were solubilized, separated by electrophoresis on SDS/12% polyacrylamide gels, and immunoblotted. Detection was by ECL. (A) GAIP is digested and not detectable after proteinase K treatment. (B) β-COP, a peripheral coat protein facing the cytoplasm, is also digested by proteinase K. (C) Calnexin, a membrane protein facing the lumen of the endoplasmic reticulum, is protected from proteinase K digestion.