Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
Mol Microbiol. 2011 Sep;81(5):1221-32. doi: 10.1111/j.1365-2958.2011.07756.x. Epub 2011 Jul 12.
The Escherichia coli dGTP triphosphohydrolase (dGTPase) encoded by the dgt gene catalyses the hydrolysis of dGTP to deoxyguanosine and triphosphate. The recent discovery of a mutator effect associated with deletion of dgt indicated participation of the triphosphohydrolase in preventing mutagenesis. Here, we have investigated the possible involvement of dgt in facilitating thymine utilization through its ability to provide intracellular deoxyguanosine, which is readily converted by the DeoD phosphorylase to deoxyribose-1-phosphate, the critical intermediate that enables uptake and utilization of thymine. Indeed, we observed that the minimal amount of thymine required for growth of thymine-requiring (thyA) strains decreased with increased expression level of the dgt gene. As expected, this dgt-mediated effect was dependent on the DeoD purine nucleoside phosphorylase. We also observed that thyA strains experience growth difficulties upon nutritional shift-up and that the dgt gene facilitates adaptation to the new growth conditions. Blockage of the alternative yjjG (dUMP phosphatase) pathway for deoxyribose-1-phosphate generation greatly exacerbated the severity of thymine starvation in enriched media, and under these conditions the dgt pathway becomes crucial in protecting the cells against thymineless death. Overall, our results suggest that the dgt-dependent pathway for deoxyribose-1-phosphate generation may operate under various cell conditions to provide deoxyribosyl donors.
大肠杆菌 dGTP 三磷酸水解酶（dGTPase）由 dgt 基因编码，催化 dGTP 水解为脱氧鸟苷和三磷酸。最近发现 dgt 缺失与突变体形成有关，表明三磷酸水解酶参与防止突变。在这里，我们通过其提供细胞内脱氧鸟苷的能力，研究了 dgt 参与促进胸腺嘧啶利用的可能性，脱氧鸟苷很容易被 DeoD 磷酸化酶转化为脱氧核糖-1-磷酸，这是允许摄取和利用胸腺嘧啶的关键中间产物。事实上，我们观察到，需要生长的最小量的胸腺嘧啶嘧啶-需要（thyA）菌株随着 dgt 基因表达水平的增加而减少。正如预期的那样，这种 dgt 介导的效应依赖于 DeoD 嘌呤核苷磷酸化酶。我们还观察到，thyA 菌株在营养物质向上转移时会遇到生长困难，并且 dgt 基因有助于适应新的生长条件。阻断替代 yjjG（dUMP 磷酸酶）途径生成脱氧核糖-1-磷酸会极大地加剧富含培养基中胸腺嘧啶饥饿的严重程度，在这些条件下，dgt 途径对于保护细胞免受无胸腺嘧啶死亡至关重要。总的来说，我们的结果表明，dgt 依赖性途径生成脱氧核糖-1-磷酸可能在各种细胞条件下发挥作用，为脱氧核糖供体提供。
