Gancedo J M
Instituto de Investigaciones Biomédicas, Unidad de Bioquímica y Genética de Levaduras, CSIC, 28029 Madrid, Spain.
Microbiol Mol Biol Rev. 1998 Jun;62(2):334-61. doi: 10.1128/MMBR.62.2.334-361.1998.
Glucose and related sugars repress the transcription of genes encoding enzymes required for the utilization of alternative carbon sources; some of these genes are also repressed by other sugars such as galactose, and the process is known as catabolite repression. The different sugars produce signals which modify the conformation of certain proteins that, in turn, directly or through a regulatory cascade affect the expression of the genes subject to catabolite repression. These genes are not all controlled by a single set of regulatory proteins, but there are different circuits of repression for different groups of genes. However, the protein kinase Snf1/Cat1 is shared by the various circuits and is therefore a central element in the regulatory process. Snf1 is not operative in the presence of glucose, and preliminary evidence suggests that Snf1 is in a dephosphorylated state under these conditions. However, the enzymes that phosphorylate and dephosphorylate Snf1 have not been identified, and it is not known how the presence of glucose may affect their activity. What has been established is that Snf1 remains active in mutants lacking either the proteins Grr1/Cat80 or Hxk2 or the Glc7 complex, which functions as a protein phosphatase. One of the main roles of Snf1 is to relieve repression by the Mig1 complex, but it is also required for the operation of transcription factors such as Adr1 and possibly other factors that are still unidentified. Although our knowledge of catabolite repression is still very incomplete, it is possible in certain cases to propose a partial model of the way in which the different elements involved in catabolite repression may be integrated.
葡萄糖及相关糖类会抑制编码利用替代碳源所需酶的基因的转录；其中一些基因也会被其他糖类如半乳糖抑制，这一过程被称为分解代谢物阻遏。不同的糖类产生信号，这些信号会改变某些蛋白质的构象，进而直接或通过调控级联反应影响受分解代谢物阻遏的基因的表达。这些基因并非都由单一的一组调控蛋白控制，而是针对不同的基因群体存在不同的阻遏回路。然而，蛋白激酶Snf1/Cat1为各个回路所共有，因此是调控过程中的核心元件。在有葡萄糖存在的情况下，Snf1不起作用，初步证据表明在这些条件下Snf1处于去磷酸化状态。然而，使Snf1磷酸化和去磷酸化的酶尚未被鉴定出来，也不清楚葡萄糖的存在如何影响它们的活性。已经确定的是，Snf1在缺乏蛋白质Grr1/Cat80、Hxk2或起蛋白磷酸酶作用的Glc7复合物的突变体中仍保持活性。Snf1的主要作用之一是解除Mig1复合物的阻遏作用，但它也是转录因子如Adr1以及可能其他尚未确定的因子发挥作用所必需的。尽管我们对分解代谢物阻遏的了解仍然非常不完整，但在某些情况下，有可能提出一个关于分解代谢物阻遏中涉及的不同元件如何整合的部分模型。
