Three factors have been identified involved in the regulation faeA from Aspergillus niger. The expression of the gene on D-xylose is mediated via X1nR, the xylanolytic transcriptional activator and depends on the xylose concentration. A decrease in the expression faeA and three other xylanolytic genes was observed with increasing xylose concentrations in a wild-type strain, whereas expression levels in a CreA mutant were not influenced. Xylose concentrations higher than 1 mM result in repression of the expression of xylanolytic genes mediated by the carbon catabolite repressor protein CreA. The expression levels of faeA and other xylanolytic genes on xylose are therefore not only determined by induction via XInR but also by repression via CreA. A third factor involved in faeA regulation responds to the presence of certain aromatic compounds with a defined ring structure such as ferulic acid and vanillic acid. The structural requirements necessary for induction have been identified. A benzene ring is present in all inducing compounds, which is substituted at C3 with a methoxy group and at C4 with a hydroxy group. C5 is not substituted, whereas different alifatic groups at Cl of the aromatic ring are allowed. Although the hydroxyl function at C4 is strongly preferred, low levels of expression have also been found with veratryl alcohol and veratric acid, two 3,4-dimethoxy compounds. Expression levels of faeA on combinations of ferulic acid and xylose are higher than on each compound alone, indicating a positive interaction between the activation by aromatic compounds and by X1nR. We acknowledge financial support of Danisco Ingredients, Brabrand, Denmark.
Fungal Genet. Newsl. 46 (Supl):
Full conference title:
Fungal Genetics Conference 20th
- Fungal Genetics Conference 20th (1999)