Glucose repression of maltase and methanol-oxidizing enzymes in the methylotrophic yeast Hansenula polymorpha: isolation and study of regulatory mutants.

Regulation of the synthesis of maltase and methanol-oxidizing enzymes by the carbon source has been analyzed in the methylotrophic yeast Hansenula polymorpha. Maltase was shown to be responsible for the growth of H. polymorpha not only on maltose, but also on sucrose. The affinity of maltase towards maltase substrates decreased in the order: 4-nitrophenyl glucoside (PNPG) < sucrose < maltose. Mutants with glucose repression-insensitive synthesis of alcohol oxidase and maltase were obtained from H. polymorpha by mutagenesis and subsequent selection on methanol medium in the presence of 2-deoxy-D-glucose. One of the isolated mutants, L63, was studied in more detail. Mutant L63 was recessive and monogenic and it was not deficient in hexokinase. Its analysis revealed that H. polymorpha most probably has a repressor protein that in the presence of glucose can down-regulate expression of both maltase and enzymes of methanol oxidation.