Swiegers Jan H, Pretorius Isak S, Bauer Florian F
The Australian Wine Research Institute, Glen Osmond, Adelaide, SA, Australia.
Curr Genet. 2006 Sep;50(3):161-71. doi: 10.1007/s00294-006-0084-z. Epub 2006 Jul 11.
In Saccharomyces cerevisiae the Ras/cAMP/PKA signalling pathway controls multiple metabolic pathways, and alterations in the intracellular concentrations of cAMP through modification of signalling pathway factors can be lethal or result in severe growth defects. In this work, the important role of Ras2p in metabolic regulation during growth on the non-fermentable carbon source glycerol is further investigated. The data show that the overexpression of RAS2 suppresses the growth defect of the glyoxylate cycle citrate synthase mutant, cit2Delta. The overexpression results in enhanced proliferation and biomass yield when cells are grown on glycerol as sole carbon source, and increases citrate synthase activity and intracellular citrate concentration. Interestingly, the suppression of cit2Delta and the enhanced proliferation and biomass yield are only observed when RAS2 is overexpressed and not in strains containing the constitutively active allele RAS2(val19). However, both RAS2 and RAS2(val19)upregulated citrate synthase activity. We propose that the RAS2 overexpression results in a combination of general upregulation of respiratory growth capacity and an increase in mitochondrial citrate/citrate synthases, which together, complement the metabolic requirements of the cit2Delta mutant. The data therefore provide new evidence for the role of Ras2p as a powerful modulator of metabolism during growth on a non-fermentable carbon source.
在酿酒酵母中，Ras/cAMP/PKA信号通路控制着多种代谢途径，通过修饰信号通路因子来改变细胞内cAMP的浓度可能是致命的，或者导致严重的生长缺陷。在这项工作中，我们进一步研究了Ras2p在以非发酵性碳源甘油为生长底物时的代谢调控中的重要作用。数据表明，RAS2的过表达抑制了乙醛酸循环柠檬酸合酶突变体cit2Δ的生长缺陷。当过表达RAS2的细胞以甘油作为唯一碳源生长时，增殖能力增强，生物量产量增加，柠檬酸合酶活性和细胞内柠檬酸浓度也增加。有趣的是，只有当RAS2过表达时，才会观察到对cit2Δ的抑制以及增殖能力增强和生物量产量增加，而在含有组成型活性等位基因RAS2(val19)的菌株中则没有观察到。然而，RAS2和RAS2(val19)都上调了柠檬酸合酶的活性。我们提出，RAS2的过表达导致呼吸生长能力普遍上调以及线粒体柠檬酸/柠檬酸合酶增加，这两者共同补充了cit2Δ突变体的代谢需求。因此，这些数据为Ras2p在以非发酵性碳源为生长底物时作为代谢的强大调节剂的作用提供了新的证据。
