CreA-mediated carbon catabolite repression of β-galactosidase formation in Aspergillus nidulans is growth rate dependent

Hedvig Ilyés, Erzsébet Fekete, Levente Karaffa, Éva Fekete, Erzsébet Sándor, Attila Szentirmai, Christian P. Kubicek

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Abstract

Carbon catabolite repression by the CreA-transcriptional repressor is widespread in filamentous fungi, but the mechanism by which glucose triggers carbon catabolite repression is still poorly understood. We investigated the hypothesis that the growth rate on glucose may control CreA-dependent carbon catabolite repression by using glucose-limited chemostat cultures and the intracellular β-galactosidase activity of Aspergillus nidulans, which is repressed by glucose, as a model system. Chemostat cultures at four different dilution rates (D=0.095, 0.068, 0.045 and 0.015 h-1) showed that formation of β-galactosidase activity is repressed at the two highest Ds, but increasingly derepressed at the lower Ds, the activity at 0.015 h -1 equalling that in derepressed batch cultures. Chemostat cultures with the carbon catabolite derepressed A. nidulans mutant strain creAΔ4 revealed a dilution-rate independent constant β-galactosidase activity of the same range as that found in the wild-type strain at D=0.015 h-1. Two other enzymes - isocitrate lyase, which is almost absent on glucose due to a CreA-independent mechanism; and galactokinase, which is formed constitutively and independent of CreA - were measured as controls. They were formed at constant activity at each dilution rate, both in the wild-type strain as well as in the carbon catabolite derepressed mutant strain. We conclude that the growth rate on glucose is a determinant of carbon catabolite repression in A. nidulans, and that below a certain growth rate carbon catabolite derepression occurs.

Original languageEnglish
Pages (from-to)147-151
Number of pages5
JournalFEMS microbiology letters
Volume235
Issue number1
DOIs
Publication statusPublished - Jun 1 2004

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Keywords

  • Aspergillus nidulans
  • Chemostat
  • CreA
  • Specific growth rate
  • β-Galactosidase

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology
  • Genetics

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