IMPROVED GENE-EXPRESSION IN ASPERGILLUS-NIDULANS

A variety of gene expression systems have been developed that utilize the promoter and transcriptional regulatory sequences derived from car bon-catabolite repressed genes for the expression of heterologous gene s. The alcA expression system of Aspergillus nidulans utilizes the pro moter and regulatory sequences derived from the alcohol dehydrogenase I (alcA) gene. Expression of the alcA gene is repressed by a DNA-bindi ng protein (CreA) in the presence of glucose and induced by ethanol un der glucose-depleted conditions. One problem encountered during the ex pression of therapeutic proteins in A. nidulans is the coexpression of secreted proteases at the time of maximal secretion of heterologous p roduct. To avoid the proteases we created an alcA promoter variant tha t is no longer sensitive to glucose repression hence could drive expre ssion at earlier time points during the fermentation, The use of this promoter variant in the expression of recombinant interleukin-6 is dis cussed. A second problem encountered during the expression of high-qua lity human therapeutic proteins in Aspergillus is aberrant glycosylati on. Lower eukaryotic systems, such as Aspergillus, tend to add highly branched mannosidic chains to heterologous secreted protein products. N-Glycans can be important for both the structure and function of spec ific glycoproteins, hence efforts are being made to in vivo alter the type and complexity of N-glycans substituted by A. nidulans.