Peroxin 3, also known as PEX3 (peroxisomal biogenesis factor 3) or TRG18, is a 373 amino acid multi-pass membrane protein that localizes to peroxisomes and belongs to the Peroxin family. Expressed ubiquitously, Peroxin 3 interacts with Peroxin 19 and is involved in peroxisome biosynthesis and membrane vesicle assembly, as well as in the maintenance of peroxisomal integrity. Additionally, Peroxin 3 acts as a docking factor for Peroxin 19 and is required for the import of peroxisomal proteins. Defects in the gene encoding Peroxin 3 are the cause of peroxisome biogenesis disorder complementation group 12 (PBD-CG12) and Zellweger syndrome (ZwS), both of which arise from a failure of peroxisomal protein import.