Constitutive appearance of peroxisomes in a regulatory mutant of the methylotrophic yeast Hansenula polymorpha.

A selection by glucosamine for mutants of Hansenula polymorpha insensitive to glucose repression of methanol assimilation is described. Constitutive synthesis of enzymes is established in standard batch cultures of glucose-grown cells. Upon prolonged glucose metabolism the phenotype is masked by catabolite inactivation and degradation of enzymes. Addition of the substrate methanol remarkably improves constitutive synthesis by preventing catabolite inactivation and delaying degradation. Regular peroxisomes of reduced number are formed in mutant cells under repressed conditions. No constitutive synthesis is detectable using ethanol as a carbon source. In addition, this alcohol is detrimental to growth of the mutants, indicating that H. polymorpha is constrained to repress synthesis of enzymes involved in the C1-metabolism when ethanol is present as a substrate.