Thomas D, Cherest H, Surdin-Kerjan Y
Laboratoire d'Enzymologie du Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Mol Cell Biol. 1989 Aug;9(8):3292-8. doi: 10.1128/mcb.9.8.3292-3298.1989.
In Saccharomyces cerevisiae, the MET25 gene encodes O-acetylhomoserine sulfhydrylase. Synthesis of this enzyme is repressed by the presence of S-adenosylmethionine (AdoMet) in the growth medium. We identified cis elements required for MET25 expression by analyzing small deletions in the MET25 promoter region. The results revealed a regulatory region, acting as an upstream activation site, that activated transcription of MET25 in the absence of methionine or AdoMet. We found that, for the most part, repression of MET25 expression was due to a lack of activation at this site, reinforced by an independent repression mechanism. The activation region contained a repeated dyad sequence that is also found in the promoter regions of other unlinked but coordinately regulated genes (MET3, MET2, and SAM2). We show that the presence of the two dyads is necessary for maximal gene expression. Moreover, we demonstrate that in addition to this transcriptional regulation, a posttranscriptional regulation, probably targeted at the 5' region of mRNA, is involved in MET25 expression.
在酿酒酵母中，MET25基因编码O - 乙酰高丝氨酸硫氢基酶。该酶的合成会受到生长培养基中S - 腺苷甲硫氨酸（AdoMet）的抑制。我们通过分析MET25启动子区域的小缺失来鉴定MET25表达所需的顺式元件。结果揭示了一个作为上游激活位点的调控区域，该区域在缺乏甲硫氨酸或AdoMet的情况下激活MET25的转录。我们发现，在很大程度上，MET25表达的抑制是由于该位点缺乏激活，同时还有一个独立的抑制机制加强了这种抑制。激活区域包含一个重复的二元序列，该序列也存在于其他不连锁但协同调控的基因（MET3、MET2和SAM2）的启动子区域。我们表明，两个二元序列的存在对于最大程度的基因表达是必需的。此外，我们证明，除了这种转录调控外，一种可能针对mRNA 5'区域的转录后调控也参与了MET25的表达。
