De Winde J H, Crauwels M, Hohmann S, Thevelein J M, Winderickx J
Departement Biologie, Katholieke Universiteit Leuven, Belgium.
Eur J Biochem. 1996 Oct 15;241(2):633-43. doi: 10.1111/j.1432-1033.1996.00633.x.
Addition of rapidly fermentable sugars to cells of the yeast Saccharomyces cerevisiae grown on nonfermentable carbon sources causes a variety of short-term and long-term regulatory effects, leading to an adaptation to fermentative metabolism. One important feature of this metabolic switch is the occurrence of extensive transcriptional repression of a large group of genes. We have investigated transcriptional regulation of the SUC2 gene encoding repressible invertase, and of HXK1, HXK2 and GLK1 encoding the three known yeast hexose kinases during transition from derepressed to repressed growth conditions. Comparing yeast strains that express various combinations of the hexose kinase genes, we have determined the importance of each of these kinases for establishing the catabolite-repressed state. We show that catabolite repression involves two distinct mechanisms. An initial rapid response is mediated through any kinase, including Glk1, which is able to phosphorylate the available sugar. In contrast, long-term repression specifically requires Hxk2 on glucose and either Hxk1 or Hxk2 on fructose. Both HXK1 and GLK1 are repressed upon addition of glucose or fructose. However, fructose repression of Hxk1 is only transient, which is in line with its preference for fructose as substrate and its requirement for long-term fructose repression. In addition, expression of HXK1 and GLK1 is regulated through cAMP-dependent protein kinase. These results indicate that sugar sensing and establishment of catabolite repression are controlled by an interregulatory network, involving all three yeast sugar kinases and the Ras-cAMP pathway.
向生长在非发酵性碳源上的酿酒酵母细胞中添加快速发酵的糖类会引发多种短期和长期的调节效应，从而导致细胞适应发酵代谢。这种代谢转换的一个重要特征是大量基因出现广泛的转录抑制。我们研究了在从去阻遏生长状态转变为阻遏生长状态的过程中，编码可阻遏性转化酶的SUC2基因以及编码三种已知酵母己糖激酶的HXK1、HXK2和GLK1基因的转录调控。通过比较表达己糖激酶基因不同组合的酵母菌株，我们确定了每种激酶对于建立分解代谢物阻遏状态的重要性。我们发现分解代谢物阻遏涉及两种不同的机制。最初的快速反应是通过任何一种能够磷酸化可用糖类的激酶介导的，包括Glk1。相比之下，长期阻遏在葡萄糖上特别需要Hxk2，在果糖上则需要Hxk1或Hxk2。添加葡萄糖或果糖后，HXK1和GLK1都会受到抑制。然而，果糖对Hxk1的抑制只是短暂的，这与其对果糖作为底物的偏好以及对长期果糖抑制的需求一致。此外，HXK1和GLK1的表达是通过cAMP依赖性蛋白激酶调节的。这些结果表明，糖类感知和分解代谢物阻遏的建立是由一个相互调节的网络控制的，该网络涉及所有三种酵母糖类激酶和Ras - cAMP途径。
