Departamento de Bioquímica y Biología Estructural, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-242, 04510 Mexico City, Mexico.
Biochem Biophys Res Commun. 2011 Jan 21;404(3):859-64. doi: 10.1016/j.bbrc.2010.12.075. Epub 2010 Dec 22.
The yeast Saccharomyces cerevisiae is able to sense the availability and quality of nitrogen sources and the intrinsic variation of amino acid disponibility for protein synthesis. When this yeast is provided with secondary nitrogen sources, transcription of genes encoding enzymes involved in their catabolism is elicited through the action of Gln3, which constitutes the main activator of the Nitrogen Catabolite Repression network (NCR). Activation of genes encoding enzymes involved in the amino acid biosynthetic pathways is achieved through the action of the GCN4-encoded transcriptional modulator whose transcriptional activation is induced at the translational level by limitation for any amino acid. Thus the role of each one of these activators had been secluded to either catabolic or biosynthetic pathways. However, some observations have suggested that under peculiar physiological conditions, Gln3 and Gcn4 could act simultaneously in order to contemporaneously increase expression of both sets of genes. This paper addresses the question of whether Gln3 and Gcn4 cooperatively determine expression of their target genes. Results presented herein show that induced expression of catabolic and biosynthetic genes when cells are grown under nitrogen derepressive conditions and amino acid deprivation is dependent on the concurrent action of Gln3 and Gcn4, which form part of a unique transcriptional complex. We propose that the combination of Gln3 and Gcn4 results in the constitution of a hybrid modulator which elicits a novel transcriptional response, not evoked when these modulators act in a non-combinatorial fashion.
酵母酿酒酵母能够感知氮源的可用性和质量，以及氨基酸用于蛋白质合成的内在可获得性的变化。当这种酵母提供了次要氮源时，通过 Gln3 的作用，引发了参与其分解代谢的酶的基因转录，Gln3 是氮分解代谢物阻遏网络（NCR）的主要激活剂。参与氨基酸生物合成途径的酶的基因转录的激活是通过 GCN4 编码的转录调节剂的作用实现的，其转录激活在翻译水平上由任何氨基酸的限制诱导。因此，这些激活剂中的每一个的作用都被隔离到分解代谢或生物合成途径中。然而，一些观察结果表明，在特殊的生理条件下，Gln3 和 Gcn4 可以同时起作用，以同时增加两组基因的表达。本文探讨了 Gln3 和 Gcn4 是否协同决定其靶基因的表达。本文提出，当细胞在氮去阻遏条件下和氨基酸缺乏下生长时，分解代谢和生物合成基因的诱导表达依赖于 Gln3 和 Gcn4 的协同作用，它们形成了一个独特的转录复合物的一部分。我们假设 Gln3 和 Gcn4 的组合导致了一个混合调节剂的构成，引发了一种新的转录反应，而当这些调节剂以非组合方式作用时，不会引发这种反应。
