PEX17P OF SACCHAROMYCES-CEREVISIAE IS A NOVEL PEROXIN AND COMPONENT OF THE PEROXISOMAL PROTEIN TRANSLOCATION MACHINERY

The Saccharomyces cerevisiae pex17-1 mutant was isolated from a screen to identify mutants defective in peroxisome biogenesis, pex17-1 and p ex17 null mutants fail to import matrix proteins into peroxisomes via both PTS1- and PTS2-dependent pathways, The PEX17 gene (formerly PAS9; Albertini, M., P. Rehling, R. Erdmann, W. Girzalsky, J.A.K.W. Kiel, M . Veenhuis, and W.-H Kunau. 1997. Cell. 89:83-92) encodes a polypeptid e of 199 amino acids with one predicted membrane spanning region and t wo putative coiled-coil structures, However, localization studies demo nstrate that Pex17p is a peripheral membrane protein located at the su rface of peroxisomes. Particulate structures containing the peroxisoma l integral membrane proteins Pex3p and Pex11p are evident in pex17 mut ant cells, indicating the existence of peroxisomal remnants (''ghosts' '). This finding suggests that pex17 null mutant cells are not impaire d in peroxisomal membrane biogenesis, Two-hybrid studies showed that P ex17p directly binds to Pex14p, the recently proposed point of converg ence for the two peroxisomal targeting signal (PTS)-dependent import p athways, and indirectly to Pex5p, the PTS1 receptor. The latter intera ction requires Pex14p, indicating the potential of these three peroxin s to form a trimeric complex. This conclusion is supported by immunopr ecipitation experiments showing that Pex14p and Pex17p coprecipitate w ith both PTS receptors in the absence of Pex13p. From these and other studies we conclude that Pex17p, in addition to Pex13p and Pex14p, is the third identified component of the peroxisomal translocation machin ery.