The peroxisomal targeting signal type1 (PTS1) receptor,PEX5,is one member of peroxins (PEXs) which are proteins required for peroxisome assembly. PEX5 and PEX7 function as receptors that recognize PTS1- and PTS2- containing proteins,respectively,and PEX5 binds PTS1 through its C-terminal 40-kDa tetratricopeptide repeat domain. It is a predominantly cytoplasmic,partly peroxisomal protein that appears to shuttle between these compartments as it mediates the import of PTS1-containing proteins. PEX5 has been reported to interact with PEX10,PEX12,PEX13,and PEX14. Defects in PEX5 are a cause of Zellweger syndrome (ZWS),which is a lethal peroxisome biogenesis disorder.