Pex19p interacts with Pex3p and Pex10p and is essential for peroxisome biogenesis in Pichia pastoris

We report the cloning and characterization of Pichia pastoris PEX19 by comp lementation of a peroxisome-deficient mutant strain. Import of peroxisomal targeting signal 1- and 2-containing peroxisomal matrix proteins is defecti ve in pex19 mutants. PEX19 encodes a hydrophilic 299-amino acid protein wit h sequence similarity to Saccharomyces cerevisiae Pex19p and human and Chin ese hamster PxF, all farnesylated proteins, as well as hypothetical protein s from Caenorhabditis elegans and Schizosaccharomyces pombe. The farnesylat ion consensus is conserved in PpPex19p but dispensable for function and app ears unmodified under the conditions tested. Pex19p localizes predominantly to the cytosolic fraction. Biochemical and two-hybrid analyses confirmed t hat Pex19p interacts with Pex3p, as seen in S, cerevisiae, but unexpectedly also with Pex10p. Two-hybrid analysis demonstrated that the amino-terminal 42 amino acids of Pex19p interact with the carboxyl-terminal 335 amino aci ds of Pex3p. In addition, the extreme carboxyl terminus of Pex19p (67 amino acids) is required for interaction with the amino-terminal 380 amino acids of Pex10p. Biochemical and immunofluorescence microscopy analyses of pex19 Delta cells identified the membrane protein Pex3p in peroxisome remnants t hat were not previously observed in S. cerevisiae. These small vesicular an d tubular (early) remnants are morphologically distinct from other Pppex mu tant (late) remnants, suggesting that Pex19p functions at an early stage of peroxisome biogenesis.