USP2 is a peroxisomal matrix protein.

<p>Immunofluorescence microscopy images of wild-type fibroblasts, containing YFP-USP2-1 (<b>A</b>), or GFP-USP2-3 (<b>B</b>) or GFP-SCP2, a peroxisomal matrix protein (<b>C</b>). Immunofluorescence microscopy was performed using antibodies against fluorescent proteins (AFP). Cells were incubated either with 1% Triton X-100, permeabilising all cellular membranes, or Digitonin (25 μg/ml), permeabilizing only the plasma membrane. Using Triton X-100, peroxisomal matrix proteins become accessible for the antibodies, as indicated by the congruent staining of the fluorophore (green) and the AFP antibody (red). Using Digitonin, only proteins facing the cytosolic compartment can interact with the antibodies, leading to a diffuse staining of the AFP antibody, when the fluorescent protein is compartmentalized into cell organelles. YFP-USP2-1 and GFP-USP2-3 could only be detected by the AFP antibody after permeabilization with Triton X-100, indicating that these proteins enter the peroxisomal lumen. Scale bar: 10 μm.