Sugar repression in the methylotrophic yeast Hansenula polymorpha studied by using hexokinase-negative, glucokinase-negative and double kinase-negative mutants |
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Authors: | Kramarenko T Karp H Järviste A Alamäe T |
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Institution: | (1) Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, 51010 Tartu, Estonia |
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Abstract: | Two glucose-phosphorylating enzymes, a hexokinase phosphorylating both glucose and fructose, and a glucose-specific glucokinase
were electrophoretically separated in the methylotrophic yeastHansenula polymorpha. Hexokinase-negative mutants were isolated inH. polymorpha by using mutagenesis, selection and genetic crosses. Regulation of synthesis of the sugar-repressed alcohol oxidase, catalase
and maltase was studied in different hexose kinase mutants. In the wild type and in mutants possessing either hexokinase or
glucokinase, glucose repressed the synthesis of maltase, alcohol oxidase and catalase. Glucose repression of alcohol oxidase
and catalase was abolished in mutants lacking both glucose-phosphorylating enzymes (i.e. in double kinase-negative mutants). Thus, glucose repression inH. polymorpha cells requires a glucose-phosphorylating enzyme, either hexokinase or glucokinase. The presence of fructose-phosphorylating
hexokinase in the cell was specifically needed for fructose repression of alcohol oxidase, catalase and maltase. Hence, glucose
or fructose has to be phosphorylated in order to cause repression of the synthesis of these enzymes inH. polymorpha suggesting that sugar repression in this yeast therefore relies on the catalytic activity of hexose kinases. |
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