CHARATERIZATION OF PEROXISOME-DEFICIENT MUTANTS OF HANSENULA-POLYMORPHA

In the methylotrophic yeast Hansenula polymorpha, approximately 25% of all methanol-utilization-defective (Mut(-)) mutants are affected in g enes required for peroxisome biogenesis (PER genes). Previously, we re ported that one group of pel mutants, termed Pim(-), are characterized by the presence of a few small peroxisomes with the bulk of peroxisom al enzymes located in the cytosol. Here, we describe a second major gr oup of pel mutants that were observed to be devoid of any peroxisome-l ike structure (Per(-)). In each Per(-) mutant, the peroxisomal methano l-pathway enzymes alcohol oxidase, catalase and dihydroxyacetone synth ase were present and active but located in the cytosol. Together, the Pim(-) and Per(-) mutant collections involved mutations in 14 differen t PER genes. Two of the genes, PERS and PER7, were represented by both dominant-negative and recessive alleles. Diploids resulting from cros ses of dominant pel strains and wild-type H. polymorpha were Mut(-) an d harbored peroxisomes with abnormal morphology. This is the first rep ort of dominant-negative mutations affecting peroxisome biogenesis.