Pernambuco M B, Winderickx J, Crauwels M, Griffioen G, Mager W H, Thevelein J M
Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit te Leuven, Flanders, Belgium.
Microbiology (Reading). 1996 Jul;142 ( Pt 7):1775-82. doi: 10.1099/13500872-142-7-1775.
Addition of glucose or fructose to cells of the yeast Saccharomyces cerevisiae grown on a nonfermentable carbon source triggers within a few minutes posttranslational activation of trehalase, repression of the CTT1 (catalase) and SSA3 (Hsp70) genes, and induction of the ribosomal protein genes RPL1, RPL25 and RPS33. By using appropriate sugar kinase mutants, it was shown that rapid glucose- or fructose-induced activation of trehalase requires phosphorylation of the sugar. On the other hand, partial induction of RPL1, RPL25 and RPS33 as well as partial repression of CTT1 and SSA3 were observed in the absence of sugar phosphorylation. In glucose-grown nitrogen-starved yeast cells readdition of a nitrogen source triggers activation of trehalase in a glucose- or fructose-dependent way, but with no apparent requirements for phosphorylation of the sugar. Repression of CTT1 and SSA3 under the same conditions was also largely dependent on the presence of the sugar and also in these cases there was a strong effect when the sugar could not be phosphorylated. Nitrogen induction of RPL1, RPL25 and RPS33 was much less dependent on the presence of the sugar, and only phosphorylated sugar caused a further increase in expression. These results show that two glucose-dependent signalling pathways, which can be distinguished on the basis of their requirement for glucose phosphorylation, appear to be involved in activation of trehalase, repression of CTT1 and SSA3 and induction of ribosomal protein genes. They also show that nutrient-induced repression of CTT1 and SSA3 is not a response to improvement of the growth conditions because the addition of nonmetabolizable sugar does not ameliorate the growth conditions. Similarly, the upshift in ribosomal protein synthesis cannot be a response to increased availability of energy or biosynthetic capacity derived from glucose, but it is apparently triggered to a significant extent by specific detection of glucose as such.
向在非发酵性碳源上生长的酿酒酵母细胞中添加葡萄糖或果糖，会在翻译后几分钟内触发海藻糖酶的激活、CTT1（过氧化氢酶）和SSA3（热休克蛋白70）基因的抑制以及核糖体蛋白基因RPL1、RPL25和RPS33的诱导。通过使用合适的糖激酶突变体，研究表明，快速的葡萄糖或果糖诱导的海藻糖酶激活需要糖的磷酸化。另一方面，在没有糖磷酸化的情况下，观察到RPL1、RPL25和RPS33的部分诱导以及CTT1和SSA3的部分抑制。在葡萄糖生长的氮饥饿酵母细胞中，重新添加氮源会以葡萄糖或果糖依赖的方式触发海藻糖酶的激活，但对糖的磷酸化没有明显要求。在相同条件下，CTT1和SSA3的抑制也很大程度上依赖于糖的存在，并且在这些情况下，当糖不能被磷酸化时也有很强的影响。RPL1、RPL25和RPS33的氮诱导对糖的存在依赖性小得多，只有磷酸化的糖会导致表达进一步增加。这些结果表明，两条基于对葡萄糖磷酸化需求可区分的葡萄糖依赖性信号通路，似乎参与了海藻糖酶的激活、CTT1和SSA3的抑制以及核糖体蛋白基因的诱导。它们还表明，营养诱导的CTT1和SSA3的抑制不是对生长条件改善的反应，因为添加不可代谢的糖并不能改善生长条件。同样，核糖体蛋白合成的上调不能是对来自葡萄糖的能量或生物合成能力可用性增加的反应，但显然在很大程度上是由对葡萄糖本身的特异性检测触发的。
