Fernández-Coll Llorenç, Cashel Michael
Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States.
Front Microbiol. 2018 Aug 3;9:1802. doi: 10.3389/fmicb.2018.01802. eCollection 2018.
During the diauxic shift, exhausts glucose and adjusts its expression pattern to grow on a secondary carbon source. Transcriptional profiling studies of glucose-lactose diauxic transitions reveal a key role for ppGpp. The amount of ppGpp depends on RelA synthetase and the balance between a strong SpoT hydrolase and its weak synthetase. In this study, mutants are used to search for synthetase or hydrolase specific regulation. Diauxic shifts experiments were performed with strains containing SpoT hydrolase and either RelA or SpoT synthetase as the sole source of ppGpp. Here, the length of the diauxic lag times is determined by the presence of ppGpp, showing contributions of both ppGpp synthetases (RelA and SpoT) as well as its hydrolase (SpoT). A balanced ppGpp response is key for a proper adaptation during diauxic shift. The effects of one or the other ppGpp synthetase on diauxic shifts are abolished by addition of amino acids or succinate, although by different mechanisms. While amino acids control the RelA response, succinate blocks the uptake of the excreted acetate via SatP. Acetate is converted to Acetyl-CoA through the pathway, producing Ac-P as intermediate. Evidence of control of the operon as well as a correlation between ppGpp and Ac-P is shown. Finally, acetylation of proteins is shown to occur during a diauxic glucose-lactose shift.
在二次生长转换期间，细胞耗尽葡萄糖并调整其表达模式以利用 secondary carbon source生长。对葡萄糖 - 乳糖二次生长转换的转录谱研究揭示了ppGpp的关键作用。ppGpp的量取决于RelA合成酶以及强大的SpoT水解酶与其较弱的合成酶之间的平衡。在本研究中，使用突变体来寻找合成酶或水解酶的特异性调控。对含有SpoT水解酶且以RelA或SpoT合成酶作为ppGpp唯一来源的菌株进行二次生长转换实验。在此，二次生长延迟时间的长短由ppGpp的存在决定，这表明ppGpp合成酶（RelA和SpoT）及其水解酶（SpoT）都有作用。平衡的ppGpp反应是二次生长转换期间适当适应的关键。添加氨基酸或琥珀酸盐可消除一种或另一种ppGpp合成酶对二次生长转换的影响，尽管其机制不同。氨基酸控制RelA反应，而琥珀酸盐通过SatP阻断排泄的乙酸盐的摄取。乙酸盐通过该途径转化为乙酰辅酶A，产生Ac - P作为中间体。显示了对该操纵子的控制证据以及ppGpp与Ac - P之间的相关性。最后，蛋白质乙酰化显示发生在葡萄糖 - 乳糖二次生长转换期间。
需注意，原文中“secondary carbon source”未明确给出具体中文释义，可根据具体专业内容进一步准确翻译，这里暂且保留英文。
