Pex19p of Hansenula
polymorpha.
Marleen Otzen,
Marten Veenhuis, Ida J. van der Klei
Eukaryotic Microbiology, University of Groningen, Kerklaan 30, Haren, 9750 AA,
The Netherlands (M.Otzen@biol.rug.nl)
Peroxisomes are single membrane-bound organelles, present in almost all eukaryotic cells. Both matrix and membrane proteins are nuclear encoded and posttranslationally transported to the organelle. The targeting of matrix proteins is dependent on either of the two known targeting signals, designated PTS1 and PTS2, which are recognized by soluble receptor proteins, Pex5p and Pex7p respectively. Numerous studies have sought for the targeting route of peroxisomal membrane proteins (PMP). These studies suggested a role for Pex19p in this process. Initial analysis of Pex19p showed that this protein is both cytosolic and peroxisomal, and that its function is essential for peroxisome biogenesis. However, the precise role of Pex19p is still under debate. We have cloned and characterized the Hansenula polymorpha PEX19 gene. In a constructed pex19 disruption strain peroxisomal structures were not detectable. In these cells matrix proteins were mislocalized in the cytosol, while PMPs were found at different subcellular locations, namely mitochondria (Pex14p) or cytosol (Pex3p, Pex10p). However, by (over)production of specific peroxins peroxisomal structures could be formed in pex19 cells. This indicates that the formation of peroxisomal structures can occur in the absence of Pex19p. A hypothetical model to explain these data and the role of Pex19p in peroxisome biogenesis will be presented.