IDENTIFICATION OF PEX13P, A PEROXISOMAL MEMBRANE-RECEPTOR FOR THE PTS1 RECOGNITION FACTOR

We have identified an S. cerevisiae integral peroxisomal membrane prot ein of M(r) of 42,705 (Pex13p) that is a component of the peroxisomal protein import apparatus. Pex13p's most striking feature is an src hom ology 3 (SH3) domain that interacts directly with yeast Pex5p (former Pas10p), the recognition factor for the COOH-terminal tripeptide signa l sequence (PTS1), but not with Pex7p (former Pas7p), the recognition factor for the NH2-terminal nonapeptide signal (PTS2) of peroxisomal m atrix proteins. Hence, Pex13p serves as peroxisomal membrane receptor for at least one of the two peroxisomal signal recognition factors. Ce lls deficient in Pex13p are unable to import peroxisomal matrix protei ns containing PTS1 and, surprisingly, also those containing PTS2. Pex1 3p deficient cells retain membranes containing the peroxisomal membran e protein Pex11p (former Pmp27p), consistent with the existence of ind ependent pathways for the integration of peroxisomal membrane proteins and for the translocation of peroxisomal matrix proteins.