Laboratory of Bioindustrial Genomics, Department of Bioindustrial Informatics and Genomics, Graduate School of Agricultural Science, Tohoku University, Aoba-ku, Sendai 981-8555, Japan.
Fungal Genet Biol. 2010 Jan;47(1):1-9. doi: 10.1016/j.fgb.2009.10.005.
Starch and maltooligosaccharides such as maltose and maltotriose induce the production of amylolytic enzymes including alpha-amylase in Aspergillus oryzae. A transcriptional activator gene amyR, required for maltose induction of amylolytic enzymes, has been cloned and characterized. The amyR gene deletion mutant showed significantly poor growth on starch medium but normal growth on maltose medium. This indicated the existence of another maltose-utilizing system, whose expression might not be controlled by amyR. We have identified a gene cluster homologous to the MAL cluster of Saccharomyces cerevisiae in the A. oryzae genome. The cluster consists of a MAL61 homolog (designated malP), a MAL62 homolog (designated malT), and a MAL63 homolog (designated malR). Overexpression of malT in A. oryzae resulted in a significant increase in intracellular alpha-glucosidase activity, and that of malP allowed S. cerevisiaemal61Delta to grow on maltose. The expression of both malP and malT genes was highly up-regulated in the presence of maltose, but malR expressed constitutively irrespective of carbon sources. Disruption of malR resulted in the loss of malP and malT expression and thus in restricted growth on maltose medium. In addition, a malP disruptant showed a significantly reduced expression of malT and malR and exhibited a growth defect on maltose similar to the malR disruptant. These results suggest that the MAL cluster of A. oryzae is responsible for the assimilation of maltose in A. oryzae.
淀粉和低聚麦芽糖，如麦芽糖和麦芽三糖，可诱导米曲霉产生包括α-淀粉酶在内的淀粉分解酶。已克隆并鉴定了一个转录激活因子基因 amyR，该基因是麦芽糖诱导淀粉分解酶产生所必需的。amyR 基因缺失突变体在淀粉培养基上的生长明显较差，但在麦芽糖培养基上的生长正常。这表明存在另一种麦芽糖利用系统，其表达可能不受 amyR 调控。我们已经在米曲霉基因组中鉴定到了与酿酒酵母 MAL 簇同源的基因簇。该簇由 MAL61 同源物（命名为 malP）、MAL62 同源物（命名为 malT）和 MAL63 同源物（命名为 malR）组成。在米曲霉中过表达 malT 导致细胞内α-葡萄糖苷酶活性显著增加，而过表达 malP 使酿酒酵母 mal61Delta 能够在麦芽糖上生长。在麦芽糖存在的情况下，malP 和 malT 基因的表达均被高度上调，但 malR 无论碳源如何均组成型表达。malR 的缺失导致 malP 和 malT 表达的丧失，从而限制了在麦芽糖培养基上的生长。此外，malP 缺失突变体表现出 malT 和 malR 的表达显著降低，并表现出类似于 malR 缺失突变体的麦芽糖生长缺陷。这些结果表明，米曲霉的 MAL 簇负责米曲霉对麦芽糖的同化。
