[Biogenesis of peroxisome--targeting signal and peroxisome assembly factor]

Peroxisome, an ubiquitous subcellular organelle in eukaryotes, functions in many crucial pathways in metabolisms such as catabolism by beta-oxidation of very long chain fatty acids, biosynthesis of etherglycerolipids, and metabolism of cholesterol. To address the question how peroxisomes are assembled in eukaryotic cells, we discuss here two topics undertaken in our laboratory. Peroxisomes are formed by posttranslational assembly mechanism; peroxisomal proteins are synthesized on free polysomes in the cytosol, mostly at their final sizes. This implies that topogenic signal(s) for import of newly synthesized polypeptides into peroxisomes reside in the internal sequence of proteins. Peroxisome-targeting signal has been noted in vivo and in vitro for enzymes such as luciferase and acyl-CoA oxidase (AOX). The topogenic signal resides at the extreme C-terminus and comprises tripeptide-Ser-Lys-Leu-COOH (SKL). Further experiments have strongly suggested that the SKL motif, Ser/Ala-Lys/Arg/His-Leu-COOH commonly found at C-termini of many peroxisomal proteins, functions as a peroxisome-targeting signal. Among several human genetic peroxisomal disorders, cerebrohepatorenal syndrome (Zellweger syndrome) is a typical, severe disease with absence of peroxisome, where a peroxisome assembly is likely to be defective. We isolated three mutants (Z24, Z65, and ZP92), recessive to wild-type cell and mutually complementary, of Chinese hamster ovary (CHO) cells that resemble the fibroblasts from Zellweger patients. To investigate molecular mechanism of peroxisome assembly and primary defects of human peroxisome-deficient disorders, we searched for the genes encoding factors that complement dysfunctions of CHO cell mutants. The mutants transfected with a pcD2-rat liver cDNA library were selected in the presence of G418.(ABSTRACT TRUNCATED AT 250 WORDS)