Carbon repression is a global regulatory mechanism in which the presence of glucose or other readily metabolized carbohydrates represses expression of genes involved in the utilization of less-favored carbon sources, respiration and gluconeogenesis. The carbon sources cause repression by affecting transcription of genes, a decrease in the translation rate of the proteins or its post-translational modification resulting in inactivation or degradation. In yeasts, the main effect of glucose takes place at the transcriptional level. The glucose repression signaling cascade in Saccharomyces cerevisiae has been widely studied, in contrast, not much is known in aspergilli. Mig1 is the major transcription factor responsible for carbon catabolite repression (CCR) in S. cerevisiae and its homologue, CreA is present in Aspergillus species. A central question is how glucose repression is triggered. Hexokinases which play an important role in yeast have not been identified as affecting glucose signaling cascade in any aspergilli. Even though one hexokinase and one glucokinase are present in A. niger. Therefore, it is not known if the transducing signal is linked to hexose phosphorylation and if a protein kinase, such as the Snf1 protein complex found in S. cerevisiae, is required for the expression of aspergillus glucose repressed genes. It is interesting to investigate whether CreA acts by itself or recruits other proteins to repress glucose-repressible promoters, like Mig1 interacting with Ssn6 and Tup1 and forming a complex. Comparative analysis of proteins involved in glucose sensing and repression pathways in S. cerevisiae, A. niger, A. nidulans and A. oryzae was performed. The analysis showed that several proteins involved in CCR in S. cerevisiae may also be present in these aspergilli. Specifically, the sensors Snf3 and Rgt2 seem to be present in A. niger, as well as homologues to the regulatory protein Grr1 and the phosphatase Glc7, involved in regulating the activity of the Snf1-complex. We grew an A. niger strain in batch fermentations using different carbon sources (glucose, xylose and glycerol). We applied DNA microarrays to conduct a transcription analysis using the Affymetrix platform with the objective of identifying global regulatory structures, mainly genes involved in CCR which are up or down regulated due to the presence of a repressing carbon source. DNA probe chips were designed by CMB staff and the analysis of the data obtained will be discussed.
Full conference title:
9th EUROPEAN CONFERENCE ON FUNGAL GENETICS
- ECFG 9th (2008)