p12^I contains a noncanonical ER retention/retrieval signal at its amino terminus. (A) Localization of the GFP-Mem, p12^I_1-15-GFP-Mem, and p12^IS10A_1-15-GFP-Mem and Red-ER in HeLa cells. (B) Localization of the GFP-Mem, p12^I_1-32-GFP-Mem, and p12^IG29S_1-32-GFP-Mem compared with Red-ER in HeLa cells. (C) Localization of GFP-Mem-KDEL and p12^I_1-5-GFP-Mem in COS-7 cells. (D) Localization of the p12^I_1-5-GFP-Mem compared with Red-ER in HeLa cells.