Vogel U, Pedersen S, Jensen K F
Institute of Biological Chemistry, University of Copenhagen, Denmark.
J Bacteriol. 1991 Feb;173(3):1168-74. doi: 10.1128/jb.173.3.1168-1174.1991.
Escherichia coli was exposed to partial pyrimidine starvation by feeding a pyrBI strain orotate as the only pyrimidine source. Subsequently, differential rates of synthesis of rRNA and of a few ribosome-associated proteins as well as the pool sizes of nucleoside triphosphates and ppGpp were measured. As the orotate concentration in the medium was reduced, the growth rate decreased and the pools of pyrimidine nucleotides, particularly UTP, declined. We did not observe the normal inverse relation between concentration of ppGpp and growth rate; rather, we observed that the ppGpp pool was low at slow growth rates. Upshifts in growth rate were made by adding uracil to a culture growing slowly on orotate. Downshifts could be provoked by adding aspartate plus glutamate to a culture growing at a high concentration of orotate. Following the upshift, both the rates of synthesis of the ribosomal components and the pool of ppGpp increased rapidly, while they all decreased after the downshift. These results are discussed in relation to the role of ppGpp in the growth rate control and the stringent response.
通过给pyrBI菌株喂食乳清酸作为唯一的嘧啶来源，使大肠杆菌暴露于部分嘧啶饥饿状态。随后，测量了rRNA和一些核糖体相关蛋白质的合成差异速率，以及核苷三磷酸和ppGpp的库大小。随着培养基中乳清酸浓度的降低，生长速率下降，嘧啶核苷酸库，特别是UTP库减少。我们没有观察到ppGpp浓度与生长速率之间正常的反比关系；相反，我们观察到在生长速率缓慢时ppGpp库较低。通过向在乳清酸上缓慢生长的培养物中添加尿嘧啶来实现生长速率的上调。通过向在高浓度乳清酸下生长的培养物中添加天冬氨酸和谷氨酸可以引发生长速率的下调。上调后，核糖体组分的合成速率和ppGpp库均迅速增加，而下调后它们都下降。结合ppGpp在生长速率控制和严谨反应中的作用对这些结果进行了讨论。
