THE IMPORT RECEPTOR FOR THE PEROXISOMAL TARGETING SIGNAL-2 (PTS2) IN SACCHAROMYCES-CEREVISIAE IS ENCODED BY THE PAS7 GENE

The import of peroxisomal matrix proteins is dependent on one of two t argeting signals, PTS1 and PTS2, We demonstrate in vivo that not only the import of thiolase but also that of a chimeric protein consisting of the thiolase PTS2 (amino acids 1-18) fused to the bacterial protein beta-lactamase is Pas7p dependent, In addition, using a combination o f several independent approaches (two-hybrid system, co-immunoprecipit ation, affinity chromatography and high copy suppression), we show tha t Pas7p specifically interacts with thiolase in vivo and in vitro, For this interaction, the N-terminal PTS2 of thiolase is both necessary a nd sufficient, The specific binding of Pas7p to thiolase does not requ ire peroxisomes, Pas7p recognizes the PTS2 of thiolase even when this otherwise N-terminal targeting signal is fused to the C-terminus of ot her proteins, i,e, the activation domain of Gal4p or GST. These result s demonstrate that Pas7p is the targeting signal-specific receptor of thiolase in Saccharomyces cerevisiae and, moreover, are consistent wit h the view that Pas7p is the general receptor of the PTS2 Our observat ion that Pas7p also interacts with the human peroxisomal thiolase sugg ests that in the human peroxisomal disorders characterized by an impor t defect for PTS2 proteins (classical rhizomelic chondrodysplasia punc tata), a functional homologue of Pas7p may be impaired.