Targeting of protein ERGIC-53 to the ER/ERGIC/cis-Golgi recycling pathway

An alternative approach to characterize loss of intracellular targeting would be to record cell surface appearance of overexpressed ERGIC-53 mutants. However, transient overexpression of wild-type ERGIC-53 leads to cell surface mislocalization in 5-10% of the transfected cells (Kappeler et al., 1994) . Surface-mislocalized ERGIC-53 protein efficiently internalizes and internalization is strongly affected by mutations in the cytoplasmic domain (Kappeler et al., 1994; Itin et al., 1995) . As a consequence the amount of ERGIC-53 at the cell surface is a combined result of loss of intracellular targeting and internalization both of which can be differentially affected by mutations.