REGULATION OF THE XYLANASE-ENCODING XLNA GENE OF ASPERGILLUS-TUBIGENSIS

A gene encoding an endo-1,4-beta-xylanase from Aspergillus tubigensis was cloned by oligonucleotide screening using oligonucleotides derived from amino acid sequence data obtained from the purified protein. The isolated gene was functional as it could be expressed in the very clo sely related fungus Aspergillus niger. The xylanase encoded by this ge ne is synthesized as a protein of 211 amino acids. After cleavage of t he presumed prepropeptide this results in a mature protein of 184 amin o acids with a molecular weight of 19 kDa and an isoelectric point of 3.6. The regulatory region of the xInA gene was studied with respect t o the response to xylan induction and carbon catabolite repression. By deletion analysis of the 5' upstream region of the gene a 158 bp regi on involved in the xylan specific induction was identified. To study t his regulatory element a reporter system for transcriptional activatin g sequences was developed that is based on the A. niger glucose oxidas e-encoding gene. From the results with this reporter system it is conc luded that this 158 bp fragment not only contains the information requ ired for induction of transcription but that it also plays a role in c arbon catabolite repression of the xlnA gene. The region directly upst ream of this fragment contains four potential CREA target sites; delet ion of this region leads to an increase in the level of transcription. These results suggest that carbon catabolite repression of the xlnA g ene is controlled at two levels, directly by repression of xlnA gene t ranscription and indirectly by repression of the expression of a trans criptional activator. This type of mechanism would be similar to the d ouble lock mechanism for the regulation of gene expression of alcA in Aspergillus nidulans. The reporter system was also used to study the r egulation of expression via the functions located on this fragment in A. niger and in A. nidulans. Essentially the same pattern of regulatio n was found in both of these hosts. Therefore, regulation of xylanase gene expression is basically conserved in all three aspergilli.