fusion was able to complement a Pex5p-defective mutant cell line, indicating that the receptor fusion wasfully functional in vivo. Protease protection assays and immunofluorescence microscopy using differential detergent extractions demonstrated that the majority of imported FLAG-Pex5p that remained associated with the peroxisome was indeed localized to the matrix although some remained associated with the peroxisome surface. The presence of surface bound FLAG-Pex5p suggested that the receptor was docked at the Pex13p, 14p, 17p complex, poised to undergo further rounds of targeting.