CARBON CATABOLITE REPRESSION IN ASPERGILLUS-NIDULANS - A REVIEW

We describe the experimental methodology that led to the discovery of the creA gene in Aspergillus nidulans. This gene codes for a transcriptional repressor mediating carbon catabolite repression in many pathways in this organism. We compare both the mode and the mechanism of action in two pathways subject to CreA-mediated repression. The genes comprising the ethanol regulon are subject to carbon catabolite repression independently of the nitrogen source, while the genes involved in proline utilization are repressed by glucose only when a repressing nitrogen source is also present. In the ethanol regulon, CreA drastically represses the expression of the positive regulatory gene alcR, thus preventing the expression of the structural genes. Direct repression of the structural genes is also existant. In the proline utilization pathway, repression operates directly at the level of the structural genes. In the ethanol regulon, CreA prevents the self-induction of alcR and the induction of the structural genes by competing with the binding of the AlcR protein. In proline gene cluster, CreA does not interfere with induction mediated by PrnA but with the activity of an unknown and more general transcription factor.