Onset of carbon catabolite repression in Aspergillus nidulans. Parallel involvement of hexokinase and glucokinase in sugar signaling.
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.
Flipphi
Michel
M
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.
van de Vondervoort
Peter J I
PJ
Ruijter
George J G
GJ
Visser
Jaap
J
Arst
Herbert N
HN
Felenbok
Béatrice
B
D000106:Acetate-CoA Ligase / Q000378:metabolism; D000818:Animals; D001233:Aspergillus nidulans / Q000201:enzymology* / Q000235:genetics; D002244:Carbon / Q000378:metabolism*; D043364:Endo-1,4-beta Xylanases; D004734:Energy Metabolism / Q000502:physiology*; D000431:Ethanol / Q000378:metabolism; D005632:Fructose / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D015966:Gene Expression Regulation, Fungal; D005941:Glucokinase / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006593:Hexokinase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014990:Xylans / Q000378:metabolism; D014994:Xylose / Q000378:metabolism; D014995:Xylosidases / Q000235:genetics / Q000378:metabolism
D005656:Fungal Proteins; D012097:Repressor Proteins; D014990:Xylans; C071237:CreA protein, Aspergillus nidulans; D005632:Fructose; D000431:Ethanol; D002244:Carbon; D014994:Xylose; D006593:Hexokinase; D005941:Glucokinase; D014995:Xylosidases; D043364:Endo-1,4-beta Xylanases; D000106:Acetate-CoA Ligase; D005947:Glucose