Cytosolic factors mediate protein insertion into the peroxisomal membrane

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Abstract
Following in vitro translation of the 22 kDa peroxisomal membrane protein (Pmp22p), gel filtration analysis of the post‐ribosomal supernatant revealed that Pmp22p forms two complexes. Complex I is of high molecular weight, results in a crosslinking product of 80 kDa, and by co‐immunoprecipitation with anti‐TCP1 antibody was identified as TRiC. In complex II Pmp22p was crosslinked to a yet unknown polypeptide of 40 kDa (P 40). This complex exhibited much higher efficiency to insert Pmp22p into the peroxisomal membrane compared to complex I. In a model we suggest that newly synthesized Pmp22p is first bound to TRiC before being transferred to P 40 which may function as a cytosolic Pmp22p receptor.