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J. Biol. Chem., Vol. 278, Issue 14, 11849-11857, April 4, 2003

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Onset of Carbon Catabolite Repression in Aspergillus nidulans
PARALLEL INVOLVEMENT OF HEXOKINASE AND GLUCOKINASE IN SUGAR SIGNALING^*

Michel Flipphi^§, Peter J. I. van de Vondervoort^¶§, George J. G. Ruijter^¶**, Jaap Visser^¶, Herbert N. Arst Jr.^§§, and Béatrice Felenbok^¶¶

From the  Institut de Génétique et Microbiologie, CNRS Unité Mixte de Recherche 8621, Université Paris-Sud XI, Centre d'Orsay, Bâtiment 409, F-91405 Orsay Cedex, France, the ^¶ Section Molecular Genetics of Industrial Microorganisms, Wageningen University, Dreijenlaan 2, NL-6703 HA Wageningen, The Netherlands, and the ^§§ Imperial College of Science, Technology and Medicine, Department of Infectious Diseases and Microbiology, DuCane Road 150, London UK-W12 0NN, United Kingdom

The role of hexose phosphorylating enzymes in the signaling of carbon catabolite repression was investigated in the filamentous fungus Aspergillus nidulans. A D-fructose non-utilizing, hexokinase-deficient (hxkA1, formerly designated frA1) strain was utilized to obtain new mutants lacking either glucokinase (glkA4) or both hexose kinases (hxkA1/glkA4). D-Glucose and D-fructose phosphorylation is completely abolished in the double mutant, which consequently cannot grow on either sugar. The glucokinase single mutant exhibits no nutritional deficiencies. Three repressible diagnostic systems, ethanol utilization (alcA and alcR genes), xylan degradation (xlnA), and acetate catabolism (facA), were analyzed in these hexose kinase mutants at the transcript level. Transcriptional repression by D-glucose is fully retained in the two single kinase mutants, whereas the hexokinase mutant is partially derepressed for D-fructose. Thus, hexokinase A and glucokinase A compensate each other for carbon catabolite repression by D-glucose in the single mutants. In contrast, both D-glucose and D-fructose repression are severely impaired for all three diagnostic systems in the double mutant. Unlike the situation in Saccharomyces cerevisiae, the hexose phosphorylating enzymes play parallel roles in glucose repression in A. nidulans.

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