Midgley J E, Gray W J
Biochem J. 1971 Apr;122(2):149-59. doi: 10.1042/bj1220149.
The rate of polymerization of ribosomal ribonucleic acid chains was estimated for steadily growing cultures of Escherichia coli M.R.E.600, from the kinetics of incorporation of exogenous [5-(3)H]uracil into completed 23S rRNA molecules. The analytical method of Avery & Midgley (1971) was used. Measurements were made at 37 degrees C, in the presence or the absence of chloramphenicol, in each of three media; enriched broth, glucose-salts or sodium lactate-salts. The rate of chain elongation of 23S rRNA was virtually constant in all media at 37 degrees C, as 24+/-4 nucleotides added/s. Accelerations in the rate of biosynthesis of rRNA by chloramphenicol in growth-limiting media are due primarily to an increase in the rate of initiation of new RNA chains, up to the rates existing in cultures growing rapidly in broth. Thus, in poorer media, only a small fraction of the available DNA-dependent RNA polymerase molecules are active at any given instant, since the chain-initiation rate is limiting in these conditions. In cultures growing rapidly in enriched broth, antibiotic inhibition caused a rise of some 12% in the rate of incorporation of exogenous uracil into total RNA. This small acceleration was due entirely to the partial stabilization of the mRNA fraction, which accumulated as 14% of the RNA formed after the addition of chloramphenicol. In cultures growing more slowly in glucose-salts or lactate-salts media, chloramphenicol caused an immediate acceleration of two- to three-fold in the overall rate of RNA synthesis. Studies by DNA-RNA hybridization showed that the synthesis of mRNA was accelerated in harmony with the other affected species. However, just over half the mRNA formed after the addition of chloramphenicol quickly decayed to acid-soluble products, whereas the remainder was more stable and accumulated in the cells. The mRNA fraction constituted about 6% of the total cellular RNA after 3h inhibition. A model was suggested to explain the partial stabilization and accumulation of the mRNA fraction and the acceleration in the rate of synthesis of mRNA when chloramphenicol was added to cultures in growth-limiting media.
根据外源[5-(3)H]尿嘧啶掺入完整23S核糖体RNA（rRNA）分子的动力学，估算了大肠杆菌M.R.E.600稳定生长培养物中核糖体核糖核酸链的聚合速率。采用了Avery和Midgley（1971年）的分析方法。在37℃下，于三种培养基（富集肉汤、葡萄糖盐培养基或乳酸盐培养基）中的每一种中，分别在有或无氯霉素存在的情况下进行测量。在37℃时，23S rRNA的链延伸速率在所有培养基中实际上是恒定的，为每秒添加24±4个核苷酸。在生长受限培养基中，氯霉素加速rRNA生物合成速率主要是由于新RNA链起始速率增加，直至达到在肉汤中快速生长的培养物中的速率。因此，在较差的培养基中，在任何给定时刻只有一小部分可用的依赖DNA的RNA聚合酶分子是活跃的，因为在这些条件下链起始速率是限制性的。在富集肉汤中快速生长的培养物中，抗生素抑制导致外源尿嘧啶掺入总RNA的速率上升约12%。这种小的加速完全是由于mRNA部分的部分稳定，其积累量占添加氯霉素后形成的RNA的14%。在葡萄糖盐或乳酸盐培养基中生长较慢的培养物中，氯霉素使RNA合成的总体速率立即加速两到三倍。DNA-RNA杂交研究表明，mRNA的合成与其他受影响的物种同步加速。然而，添加氯霉素后形成的mRNA中略多于一半迅速降解为酸溶性产物，而其余部分更稳定并在细胞中积累。抑制3小时后，mRNA部分约占细胞总RNA的6%。提出了一个模型来解释当在生长受限培养基中向培养物中添加氯霉素时，mRNA部分的部分稳定和积累以及mRNA合成速率的加速。
