Shen V, Bremer H
J Bacteriol. 1977 Jun;130(3):1098-108. doi: 10.1128/jb.130.3.1098-1108.1977.
The synthesis of ribosomal ribonucleic acid (rRNA), transfer RNA (tRNA) and messenger RNA (mRNA) was measured in Escherichia coli B/r after the addition of 100 mug of chloramphenicol (CAM) per ml to cultures growing either in one of three minimal media (succinate, glycerol, or glucose) or in one of the same three media supplemented with 20 amino acids. (i) During CAM treatment, rRNA and tRNA were synthesized in the same relative proportions (85:15) as during exponential growth. The faster accumulation of tRNA relative to rRNA in CAM was due to a decreased stability of rRNA that is synthesized in the presence of or immediately before the addition of CAM. (ii) CAM stimulated the synthesis of rRNA and tRNA two- to eightfold. The results fell into two groups; one group was from studies done in minimal media and the other was from amino acid-supplemented media. In each group the stimulation decreased with increasing growth rate of the culture during exponential growth before the addition of CAM; however, the stimulation in minimal media was lower than that in amino acid-supplemented media. (iii) CAM caused an increase in the proportion of rRNA and tRNA synthesis and a corresponding decrease in the proportion of mRNA synthesis. In minimal media, the residual proportion of mRNA synthesis after CAM treatment was 10 to 15% of total RNA synthesis; in amino acid-supplemented media this proportion was 0 to 10%. In either case, the residual proportion of mRNA synthesis was independent of the proportions observed during exponential growth in these media. (iv) The absolute rate of mRNA synthesis decreased severalfold with the addition of CAM; i.e., the rate of synthesis of rRNA and tRNA was increased at the expense of mRNA synthesis. (v) During exponential growth, the fraction of the instantaneous rate of total RNA synthesis that corresponds to mRNA is a function of both the growth rate and the presence or absence of amino acids in the growth medium: in the absence of amino acids, this fraction decreased with increasing growth rate; in the presence of amino acids, the fraction increased slightly with growth rate. These results are consistent with a regulation of rRNA and tRNA synthesis at the transcriptional level, e.g., with a CAM-induced increase in the affinity of RNA polymerase for the rRNA and tRNA promoters. The results also suggest the occurrence of a regulation of RNA polymerase enzyme activity, i.e., of an activation of RNA polymerase that is inactive during exponential growth. A distinction between these alternatives requires measurements of the rRNA chain growth rates during CAM treatment.
向在三种基本培养基（琥珀酸盐、甘油或葡萄糖）之一中生长的大肠杆菌B/r培养物，或在添加了20种氨基酸的相同三种培养基之一中生长的培养物中，每毫升加入100微克氯霉素（CAM）后，测定核糖体核糖核酸（rRNA）、转运核糖核酸（tRNA）和信使核糖核酸（mRNA）的合成情况。（i）在CAM处理期间，rRNA和tRNA以与指数生长期间相同的相对比例（85:15）合成。在CAM存在下或添加CAM之前立即合成的rRNA稳定性降低，导致在CAM处理期间tRNA相对于rRNA积累更快。（ii）CAM刺激rRNA和tRNA的合成增加了2至8倍。结果分为两组；一组来自在基本培养基中进行的研究，另一组来自添加了氨基酸的培养基。在每组中，在添加CAM之前的指数生长期间，随着培养物生长速率的增加，刺激作用降低；然而，基本培养基中的刺激作用低于添加了氨基酸的培养基。（iii）CAM导致rRNA和tRNA合成比例增加，而mRNA合成比例相应降低。在基本培养基中，CAM处理后mRNA合成的残留比例为总RNA合成的10%至15%；在添加了氨基酸的培养基中，该比例为0%至10%。在任何一种情况下，mRNA合成的残留比例都与这些培养基中指数生长期间观察到的比例无关。（iv）添加CAM后，mRNA合成的绝对速率降低了几倍；即，rRNA和tRNA的合成速率增加是以mRNA合成的减少为代价的。（v）在指数生长期间，对应于mRNA的总RNA合成瞬时速率的分数是生长速率以及生长培养基中是否存在氨基酸的函数：在没有氨基酸的情况下，该分数随着生长速率的增加而降低；在有氨基酸的情况下，该分数随着生长速率略有增加。这些结果与rRNA和tRNA合成在转录水平上的调节一致，例如，与CAM诱导的RNA聚合酶对rRNA和tRNA启动子亲和力增加一致。结果还表明存在RNA聚合酶酶活性的调节，即在指数生长期间无活性的RNA聚合酶的激活。区分这些可能性需要测量CAM处理期间rRNA链的生长速率。
