Molecular Cloning and Transcriptional Regulation of the Aspergillus nidulans xlnD Gene Encoding a β-Xylosidase

The xlnD gene encoding the 85-kDa β-xylosidase was cloned from Aspergillus nidulans. The deduced primary structure of the protein exhibits considerable similarity to the primary structures of the Aspergillus niger and Trichoderma reesei β-xylosidases and some similarity to the primary structures of the class 3 β-glucosidases. xlnD is regulated at the transcriptional level; it is induced by xylan and d-xylose and is repressed by d-glucose. Glucose repression is mediated by the product of the creA gene. Although several binding sites for the pH regulatory protein PacC were found in the upstream regulatory region, it was not clear from a Northern analysis whether PacC is involved in transcriptional regulation of xlnD.