ROLE OF THE PAS1 GENE OF PICHIA-PASTORIS IN PEROXISOME BIOGENESIS

Several groups have reported the cloning and sequencing of genes invol ved in the biogenesis of yeast peroxisomes. Yeast strains bearing muta tions in these genes are unable to grow on carbon sources whose metabo lism requires peroxisomes, and these strains lack morphologically norm al peroxisomes. We report the cloning of Pichia pastoris PAS1, the hom ologue (based on a high level of protein sequence similarity) of the S accharomyces cerevisiae PAS1. We also describe the creation and charac terization of P. pastoris pas1 strains. Electron microscopy on the P. pastoris pas1 cells revealed that they lack morphologically normal per oxisomes, and instead contain membrane-bound structures that appear to be small, mutant peroxisomes, or ''peroxisome ghosts.'' These ''ghost s'' proliferated in response to induction on peroxisome requiring carb on sources (oleic acid and methanol), and they were distributed to dau ghter cells. Biochemical analysis of cell lysates revealed that peroxi somal proteins are induced normally in pas1 cells. Peroxisome ghosts f rom pas1 cells were purified on sucrose gradients, and biochemical ana lysis showed that these ghosts, while lacking several peroxisomal prot eins, did import varying amounts of several other peroxisomal proteins . The existence of detectable peroxisome ghosts in P. pastoris pas1 ce lls, and their ability to import some proteins, stands in contrast wit h the results reported by Erdmann et al. (1991) for the S. cerevisiae pas1 mutant, in which they were unable to detect peroxisome-like struc tures. We discuss the role of PAS1 in peroxisome biogenesis in light o f the new information regarding peroxisome ghosts in pas1 cells.