intracellular localization function and dysfunction of the peroxisometargeting signal type 2 receptor pex7p in mammalian cells we previously isolated and characterized a chinese hamster ovary cho cell mutant zpg207 that is defective in import of proteins carrying a peroxisometargeting signal type 2 pts2 nonapeptide herein we have cloned chinese hamster cl pex7 encoding the pts2 receptor clpex7p consists of 318 amino acids shorter than human pex7p by 5 residues showing 91 and 30 identity with pex7p from humans and the yeast saccharomyces cerevisiae respectively expression of clpex7 rescued the impaired pts2 import in pex7 zpg207 mutation in zpg207 pex7 was determined by reverse transcription pcr a gtoa transition caused a 1amino acid substitution w221ter we investigated the molecular dysfunction of pex7p variants in mammals including pex7pw221ter and pex7p with one site mutation at g217r a218v or l292ter which frequently occurs in the human fatal genetic peroxisomal disease rhizomelic chondrodysplasia punctata showing a cell phenotype of pts2 import defect all types of the mutations affected pex7p in binding to both pts2 cargo protein and the longer isoform of pts1 receptor pex5pl that is responsible for transport of the pex7ppts2 complex subcellular fractionation and protease protection studies demonstrated bimodal distribution of pex7p between the cytoplasm and peroxisomes in cho and human cells moreover expression of pex5pl but not of the shorter isoform pex5ps enhanced translocation of pex7ppts2 proteins into peroxisomes thereby implying that both pts receptors shuttle between peroxisomes and the cytosol furthermore a clpex7p mutant with a deletion of 7 amino acids from the n terminus retained peroxisomerestoring activity whereas an 11amino acid truncation abrogated the activity clpex7p with a cterminal 9 amino acid truncation comprising residues 1309 maintained the activity whereas a 14amino acid shorter form lacking several amino acids of the sixth wd motif lost the activity therefore nearly the full length of pex7p including all wd motifs is required for its function