Peroxisomal Biogenesis Factor 4 (PEX4)

Peroxin4 (pex4) , an apparent ubiquitin-conjugating enzyme, interacts with PEX22. Expression of both Arabidopsis genes together complemented yeast pex4 or pex22 mutant defects, whereas expression of either gene individually failed to rescue the corresponding yeast mutant. Therefore, it is likely that the Arabidopsis proteins can function similarly to the yeast PEX4-PEX22 complex, with PEX4 ubiquitinating substrates and PEX22 tethering PEX4 to the peroxisome. However, the severe sucrose dependence of the pex4 pex22 mutant is not accompanied by correspondingly strong defects in peroxisomal matrix protein import, suggesting that this peroxin pair may have novel plant targets in addition to those important in fungi. Isocitrate lyase is stabilized in pex4 pex22, indicating that PEX4 and PEX22 may be important during the remodeling of peroxisome matrix contents as glyoxysomes transition to leaf peroxisomes.