Künzler M, Paravicini G, Egli C M, Irniger S, Braus G H
Mikrobiologisches Institut, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland.
Gene. 1992 Apr 1;113(1):67-74. doi: 10.1016/0378-1119(92)90670-k.
In Saccharomyces cerevisiae, two differently regulated 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase (DAHPS; EC 4.1.2.15) isoenzymes carry out the first step in the shikimate pathway. Mutations in both genes are necessary to cause aromatic amino acid (aa) auxotrophy, since one isoenzyme alone is sufficient to produce enough DAHP for normal growth of the cells. The phenylalanine-inhibited DAHPS is encoded by the previously isolated and characterized ARO3 gene. Here, we report the cloning and characterization of the ARO4 gene, encoding the second DAHPS, which is inhibited by tyrosine. The aa sequence of the ARO4 gene product reveals 76% similarity to the ARO3-encoded isoenzyme and 66 and 73% to the three DAHPS isoenzymes from Escherichia coli. ARO4 gene expression is regulated by the general control system of aa biosynthesis. As in the case of the ARO3 gene, a single GCN4-recognition element in the promoter is responsible for derepression of the ARO4 gene under aa starvation conditions. However, in contrast to the situation in the isogene, ARO3, GCN4 does not contribute to the basal level of ARO4 transcription under nonderepressing conditions.
在酿酒酵母中，两种受不同调控的3-脱氧-D-阿拉伯庚酮糖-7-磷酸（DAHP）合酶（DAHPS；EC 4.1.2.15）同工酶催化莽草酸途径的第一步反应。两个基因的突变对于导致芳香族氨基酸营养缺陷型是必需的，因为单独一种同工酶就足以产生足够的DAHP以满足细胞的正常生长。苯丙氨酸抑制的DAHPS由先前分离和鉴定的ARO3基因编码。在此，我们报道了编码第二种DAHPS（受酪氨酸抑制）的ARO4基因的克隆和鉴定。ARO4基因产物的氨基酸序列与ARO3编码的同工酶有76%的相似性，与大肠杆菌的三种DAHPS同工酶分别有66%和73%的相似性。ARO4基因的表达受氨基酸生物合成的一般控制系统调控。与ARO3基因的情况一样，启动子中的单个GCN4识别元件负责在氨基酸饥饿条件下解除对ARO4基因的抑制。然而，与同基因ARO3的情况不同，在非抑制条件下，GCN4对ARO4转录的基础水平没有贡献。
