Characterization of the Yeast and Human Receptors for the Carboxy-terminal Tripeptide Peroxisomal Targeting Signal

Proteins resident in the peroxisomal membrane and matrix are encoded by nuclear genes and imported posttranslationally (Lazarow and Fujiki 1985). Genetic and biochemical evidence in yeast and humans supports the notion that there are at least two pathways for the import of proteins into the peroxisomal matrix, each dependent on the use of a specific peroxisomal targeting signal (PTS) and a cognate receptor (Subramani 1993). Whether these import pathways are completely distinct or converge to use the same translocation machinery is unknown. Earlier work in mammalian cells has identified a carboxy-terminal, tripeptide sequence (S/A/C-K/R/H-L/M), called PTS1, as the major targeting signal used for the sorting of proteins into the peroxisomal matrix (Gould et al. 1989). A second sequence, called PTS2, is used by a smaller subset of proteins represented by rat peroxisomal 3-ketoacyl-CoA thiolase. This PTS is an amino-terminal undecapeptide (MHRLQVVLGHL) that is sometimes cleaved proteolytically following import of the...