Topogenesis of peroxisomal proteins does not require a functional cytoplasm-to-vacuole transport

Folded and even oligomeric proteins can be imported from the cytosol into vacuoles and into peroxisomes. Pro-aminopeptidase I (prAPI) oligomerizes into a dodecamer and is imported into the vacuole via the cytoplasm-to-vacuole transport (cvt) pathway. How peroxisomes accommodate folded proteins is completely unknown. Peroxisome biogenesis and cvt do not only share the import of folded protein complexes but also show mechanistic parallels such as the employment of ubiquitin conjugation systems. In search for a genetic overlap, selected cvt and autophagocytosis (atg) mutants were tested for defects in peroxisome biogenesis. Most of the mutants did not exhibit a mislocalization of peroxisomal matrix proteins to the cytosol which would be typical of a defect in the peroxisome biogenesis. However, two mutants, Δatg14 and Δcvt4/vam6, displayed a general growth defect and Δcvt8/vps41 showed cytosolic mislocalization not only of peroxisomal but also of mitochondrial proteins, indicating a more general defect in organelle biogenesis. Our data do not provide evidence for a genetic overlap of the import pathway for peroxisomal proteins and the cvt pathway.