Regulation of the amylolytic and (hemi-)cellulolytic genes in aspergilli

Filamentous fungi produce high levels of polysaccharide-degrading enzymes a nd are frequently used for the production of industrial enzymes. Because of the high secretory capacity for enzymes, filamentous fungi are effective h osts for the production of foreign proteins. Genetic studies with Aspergill us nidulans have shown pathway-specific regulatory systems that control a s et of genes that must be expressed to catabolize particular substrates. Bes ides the pathway-specific regulation, wide domain regulatory systems exist that affect a great many individual genes in different pathways. A molecula r analysis of various regulated systems has confirmed the formal models der ived from purely genetic data. In general, many genes are subject to more t han one regulatory system. In this article, we describe two transcriptional activators, AmyR and XlnR, and an enhancer, Hap complex, in view of their regulatory roles in the expression of the amylolytic and (hemi-)cellulolyti c genes mainly in aspergilli. The amyR gene has been isolated as a transcri ptional activator involved in the expression of amylolytic genes from A. or yzae, A. niger, and A. nidulans, and the xlnR gene, which has been isolated from A. niger and A. oryzae, activates the expression of xylanolytic genes as well as some cellulolytic genes in aspergilli. Both AmyR and XlnR have a typical zinc binuclear cluster DNA-binding domain at their N-terminal reg ions. Hap complex, a CCAAT-binding complex, enhances the overall promoter a ctivity and increases the expression levels of many fungal genes, including the Taka-amylase A gene. Hap complex comprises three subunits, HapB, HapC, and HapE, in A. nidulans and A. oryzae as well as higher eukaryotes, where as HAP complex in Saccharomyces cerevisiae and Kluyveromyces lactis has the additional subunit, Hap4p, which is responsible for the transcriptional ac tivation. Hap complex is suggested to enhance transcription by remodeling t he chromatin structure. The regulation of gene expression in filamentous fu ngi of industrial interest could follow basically the same general principl es as those discovered in A. nidulans. The knowledge of regulation of gene expression in combination with traditional genetic techniques is expected t o be increasingly utilized for strain breeding. Furthermore, this knowledge provides a basis for the rational application of transcriptional regulator s for biotechnological processes in filamentous fungi.