Common fixation-permeabilization methods cause artifactual localization of a type II transmembrane protein.

We found that a localization artifact can arise from common immunofluorescence methods. Specifically, cell fixation and permeabilization can cause mislocalization of a type II membrane-bound protein, ER mannosidase I, from its native localization in vesicles to the Golgi complex. Live cell microscopy and interestingly also mild cell fixation with paraformaldehyde without membrane permeabilization do not present this artifact.