Baracchini E, Bremer H
Molecular Program, University of Texas, Richardson 75083-0688.
J Biol Chem. 1991 Jun 25;266(18):11753-60.
The effects of extra, plasmid-borne rRNA genes on the synthesis rate of rRNA in Escherichia coli were examined by measuring the fraction of total RNA synthesis that is rRNA and tRNA (rs/rt), the cytoplasmic concentration of guanosine tetraphosphate (ppGpp), and the absolute rates of RNA and protein synthesis. Experiments were carried out in different growth media and with two different strains of E. coli, B/r and K-12. The results indicated: 1) increased rrn gene dosage from either intact or defective rrn genes reduced bacterial growth rates and ribosome activity (protein synthesis rate/average ribosome), and increased rs/rt. 2) Extra intact, but not extra defective, plasmid-borne rrn genes caused the level of ppGpp to be increased in comparison to the pBR322-carrying control strain. 3) As a function of ppGpp, rs/rt was increased with either intact or defective rrn genes. 4) The rRNA synthesis rate/rrn gene was reduced in the presence of extra rrn genes; this reduction in gene activity was greater with intact than with defective rrn genes. An analysis of these results showed that they are consistent with the ppGpp hypothesis of rRNA control but not with a feedback effector role of translating ribosomes.
通过测量rRNA和tRNA在总RNA合成中所占的比例（rs/rt）、鸟苷四磷酸（ppGpp）的胞质浓度以及RNA和蛋白质合成的绝对速率，研究了额外的、质粒携带的rRNA基因对大肠杆菌rRNA合成速率的影响。实验在不同的生长培养基中，使用两种不同的大肠杆菌菌株B/r和K - 12进行。结果表明：1）完整或缺陷rrn基因的rrn基因剂量增加会降低细菌生长速率和核糖体活性（蛋白质合成速率/平均核糖体），并增加rs/rt。2）与携带pBR322的对照菌株相比，额外完整而非额外缺陷的质粒携带rrn基因会使ppGpp水平升高。3）作为ppGpp的函数，无论rrn基因完整或有缺陷，rs/rt都会增加。4）在存在额外rrn基因的情况下，每个rrn基因的rRNA合成速率降低；完整rrn基因的这种基因活性降低比缺陷rrn基因更大。对这些结果的分析表明，它们与rRNA控制的ppGpp假说一致，但与翻译核糖体的反馈效应作用不一致。
