Tsukagoshi Norihiro, Kobayashi Tetsuo, Kato Masashi
Department of Biological Mechanisms and Functions, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
J Gen Appl Microbiol. 2001 Feb;47(1):1-19. doi: 10.2323/jgam.47.1.
Filamentous fungi produce high levels of polysaccharide-degrading enzymes and are frequently used for the production of industrial enzymes. Because of the high secretory capacity for enzymes, filamentous fungi are effective hosts for the production of foreign proteins. Genetic studies with Aspergillus nidulans have shown pathway-specific regulatory systems that control a set of genes that must be expressed to catabolize particular substrates. Besides the pathway-specific regulation, wide domain regulatory systems exist that affect a great many individual genes in different pathways. A molecular analysis of various regulated systems has confirmed the formal models derived from purely genetic data. In general, many genes are subject to more than 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-)cellulolytic genes mainly in aspergilli. The amyR gene has been isolated as a transcriptional activator involved in the expression of amylolytic genes from A. oryzae, 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 regions. Hap complex, a CCAAT-binding complex, enhances the overall promoter activity 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, whereas HAP complex in Saccharomyces cerevisiae and Kluyveromyces lactis has the additional subunit, Hap4p, which is responsible for the transcriptional activation. Hap complex is suggested to enhance transcription by remodeling the chromatin structure. The regulation of gene expression in filamentous fungi of industrial interest could follow basically the same general principles as those discovered in A. nidulans. The knowledge of regulation of gene expression in combination with traditional genetic techniques is expected to be increasingly utilized for strain breeding. Furthermore, this knowledge provides a basis for the rational application of transcriptional regulators for biotechnological processes in filamentous fungi.
丝状真菌能产生大量多糖降解酶，常用于工业酶的生产。由于其强大的酶分泌能力，丝状真菌是生产外源蛋白的有效宿主。对构巢曲霉的遗传学研究揭示了途径特异性调控系统，该系统控制着一组在分解特定底物时必须表达的基因。除了途径特异性调控外，还存在广泛的调控系统，影响着不同途径中的许多单个基因。对各种调控系统的分子分析证实了从纯遗传数据得出的形式模型。一般来说，许多基因受到不止一种调控系统的作用。在本文中，我们描述了两种转录激活因子AmyR和XlnR，以及一种增强子Hap复合物，鉴于它们在主要曲霉属中淀粉分解和（半）纤维素分解基因表达中的调控作用。amyR基因已被分离出来，作为参与米曲霉、黑曲霉和构巢曲霉淀粉分解基因表达的转录激活因子，而从黑曲霉和米曲霉中分离出的xlnR基因，可激活曲霉属中木聚糖分解基因以及一些纤维素分解基因的表达。AmyR和XlnR在其N端区域都有一个典型的锌双核簇DNA结合结构域。Hap复合物是一种结合CCAAT的复合物，可增强整体启动子活性，并提高许多真菌基因的表达水平，包括米曲霉淀粉酶A基因。在构巢曲霉、米曲霉以及高等真核生物中，Hap复合物由三个亚基HapB、HapC和HapE组成，而酿酒酵母和乳酸克鲁维酵母中的HAP复合物还有额外的亚基Hap4p，它负责转录激活。有人认为Hap复合物通过重塑染色质结构来增强转录。具有工业价值的丝状真菌中的基因表达调控基本上可能遵循与在构巢曲霉中发现的相同的一般原则。基因表达调控知识与传统遗传技术相结合，有望越来越多地用于菌株育种。此外，这些知识为在丝状真菌生物技术过程中合理应用转录调节因子提供了基础。
