Mutation of the C-terminal ER-retention/retrieval sequence in β4 liberates β4 to the surface.

(A) Expression pattern of the cotransfected FAP-BKα (unlabeled; not visualized), β4-Ala mutant (anti-β4 immunocytochemistry: green) and mRFP- KDEL (intrinsic fluorescence; red) in fixed, permeabilized HEK-293 cells. (B) Same as (A) but under non-permeabilized conditions. (C) Same as for (A) but for β4-polySer mutant under permeabilized conditions. (D) Same as (C) but under non-permeabilized conditions. Scale bar = 10 µm (A–D).