Institut für Mikrobiologie & Genetik, Georg-August-Universität, Grisebachstr. 8, D-37077 Göttingen, Germany.
Fungal Genet Biol. 2012 Jun;49(6):443-54. doi: 10.1016/j.fgb.2012.04.003. Epub 2012 Apr 26.
The filamentous fungus Aspergillus nidulans carries a single gene for the S-adenosylmethionine (SAM) synthetase SasA, whereas many other organisms possess multiple SAM synthetases. The conserved enzyme catalyzes the reaction of methionine and ATP to the ubiquitous methyl group donor SAM. SAM is the main methyl group donor for methyltransferases to modify DNA, RNA, protein, metabolites, or phospholipid target substrates. We show here that the single A. nidulans SAM synthetase encoding gene sasA is essential. Overexpression of sasA, encoding a predominantly cytoplasmic protein, led to impaired development including only small sterile fruiting bodies which are surrounded by unusually pigmented auxiliary Hülle cells. Hülle cells are the only fungal cell type which does not contain significant amounts of SasA. Sterigmatocystin production is altered when sasA is overexpressed, suggesting defects in coordination of development and secondary metabolism. SasA interacts with various metabolic proteins including methionine or mitochondrial metabolic enzymes as well as proteins involved in fungal morphogenesis. SasA interaction to histone-2B might reflect a putative epigenetic link to gene expression. Our data suggest a distinct role of SasA in coordinating fungal secondary metabolism and development.
丝状真菌构巢曲霉携带一个用于 S-腺苷甲硫氨酸（SAM）合成酶 SasA 的单一基因，而许多其他生物体则具有多个 SAM 合成酶。这种保守的酶催化蛋氨酸和 ATP 反应生成普遍存在的甲基供体 SAM。SAM 是甲基转移酶修饰 DNA、RNA、蛋白质、代谢物或磷脂靶底物的主要甲基供体。我们在这里表明，单一的构巢曲霉 SAM 合成酶编码基因 sasA 是必需的。sasA 的过表达，编码一种主要存在于细胞质中的蛋白质，导致发育受损，包括只有小的无菌子实体，这些子实体被异常着色的辅助 Hülle 细胞包围。Hülle 细胞是唯一不含有大量 SasA 的真菌细胞类型。当 sasA 过表达时，麦角固醇的产生发生改变，这表明在发育和次生代谢的协调方面存在缺陷。SasA 与各种代谢蛋白相互作用，包括蛋氨酸或线粒体代谢酶以及参与真菌形态发生的蛋白质。SasA 与组蛋白-2B 的相互作用可能反映了与基因表达的潜在表观遗传联系。我们的数据表明 SasA 在协调真菌次生代谢和发育方面具有独特的作用。
