Denis V, Daignan-Fornier B
Institut de Biochimie et Génétique Cellulaires, Bordeaux, France.
Mol Gen Genet. 1998 Aug;259(3):246-55. doi: 10.1007/s004380050810.
Glutamine, glycine and 10-formyl tetrahydrofolate are consumed during de novo purine biosynthesis. We have found that, in Saccharomyces cerevisiae, synthesis of these cosubstrates is coregulated with synthesis of enzymes of the purine biosynthetic pathway. Analysis of three genes required for synthesis of glutamine, glycine and 10-formyl tetrahydrofolate (GLN1, SHM2 and MTD1, respectively) shows that their expression is repressed by adenine and requires the transcription factors Baslp and Bas2p. Northern analysis reveals that regulation of SHM2 and MTD1 expression by adenine takes place at the transcriptional level. We also show that Bas1p and Bas2p bind in vitro to the promoters of the SHM2 and MTD1 genes, and that mutations in the consensus Bas1p binding sequences strongly affect expression of these genes in vivo. Finally, we have found that a SHM2-lacZ fusion is expressed at a significantly higher level in a bas2-2 disrupted strain than in bas1-2 or bas1-2 bas2-2 mutant strains. The BAS1-dependent, BAS2-independent expression of SHM2-lacZ suggests that, in the absence of Bas2p, Bas1p can interact with another protein partner to activate SHM2 expression.
在嘌呤从头合成过程中，谷氨酰胺、甘氨酸和10-甲酰四氢叶酸会被消耗。我们发现在酿酒酵母中，这些辅酶底物的合成与嘌呤生物合成途径中酶的合成是共同调控的。对合成谷氨酰胺、甘氨酸和10-甲酰四氢叶酸所需的三个基因（分别为GLN1、SHM2和MTD1）的分析表明，它们的表达受到腺嘌呤的抑制，并且需要转录因子Baslp和Bas2p。Northern分析显示，腺嘌呤对SHM2和MTD1表达的调控发生在转录水平。我们还表明，Bas1p和Bas2p在体外与SHM2和MTD1基因的启动子结合，并且在Bas1p结合序列共有序列中的突变会强烈影响这些基因在体内的表达。最后，我们发现SHM2-lacZ融合蛋白在bas2-2缺失菌株中的表达水平明显高于bas1-2或bas1-2 bas2-2突变菌株。SHM2-lacZ的BAS1依赖性、BAS2非依赖性表达表明，在没有Bas2p的情况下，Bas1p可以与另一种蛋白质伴侣相互作用以激活SHM2的表达。
