Little R, Fiil N P, Dennis P P
J Bacteriol. 1981 Jul;147(1):25-35. doi: 10.1128/jb.147.1.25-35.1981.
A partial restriction of ribonucleic acid (RNA) polymerase activity has been used to dissociate the coordinate synthesis of ribosomal proteins and subunits of RNA polymerase and to identify transcriptional and post-transcriptional control signals which regulate the expression of these component genes. Within the beta operon [which has the genetic organization: promoter (p beta), rplJ (L10), r;lL (L7/L12), attenuator, rpoB (beta), rpoC (beta'), terminator], the restriction caused a disproportionate increase between proximal and distal gene transcriptions; the transcriptional intensities of the proximal ribosomal protein genes and the distal RNA polymerase genes were elevated about two- and fourfold, respectively. Transcription within the operon containing four ribosomal protein genes and the RNA polymerase alpha gene was also enhanced, whereas transcription within operons containing only ribosomal protein genes was virtually unaffected by the restriction. It was thus concluded that the mechanisms controlling transcription initiation or attenuation or both in operons containing RNA polymerase subunit genes are coupled to the global rate of RNA synthesis. By introducing the composite ColE1 plasmid pJC701 carrying the proximal portion of the L10 operon, including the beta subunit gene, it was possible to achieve a 10- and a 30-fold range in the transcriptional intensities of the genes specifying L10 and L7/L12 and beta, respectively. Under these conditions, the relative synthesis rates of L7/L12 and beta protein varied by less than 2-fold and by about 15-fold, respectively. These observations corroborate the existence of a post-transcriptional mechanism which severely restricts translation of excess L7/L12 and L10 ribosomal protein messenger RNA; this mechanism is probably important in maintaining the balanced synthesis of ribosome components under conditions in which their messenger RNA levels are dissociated. Furthermore, the observed reduction in the translation efficiency of beta subunit messenger RNA may be related to an inhibitory effect caused by accumulation of RNA polymerase assembly intermediates.
核糖核酸（RNA）聚合酶活性的部分限制已被用于解离核糖体蛋白与RNA聚合酶亚基的协同合成，并识别调节这些组成基因表达的转录和转录后控制信号。在β操纵子内[其基因组织为：启动子（pβ）、rplJ（L10）、rplL（L7/L12）、弱化子、rpoB（β）、rpoC（β'）、终止子]，这种限制导致近端和远端基因转录之间不成比例的增加；近端核糖体蛋白基因和远端RNA聚合酶基因的转录强度分别提高了约两倍和四倍。包含四个核糖体蛋白基因和RNA聚合酶α基因的操纵子内的转录也增强了，而仅包含核糖体蛋白基因的操纵子内的转录实际上不受这种限制的影响。因此得出结论，在含有RNA聚合酶亚基基因的操纵子中，控制转录起始或弱化或两者的机制与RNA合成的整体速率相关联。通过引入携带L10操纵子近端部分（包括β亚基基因）的复合ColE1质粒pJC701，分别使指定L10、L7/L12和β的基因的转录强度达到了10倍和30倍的范围。在这些条件下，L7/L12和β蛋白的相对合成速率分别变化小于2倍和约15倍。这些观察结果证实了存在一种转录后机制，该机制严重限制过量的L7/L12和L10核糖体蛋白信使RNA的翻译；这种机制可能在其信使RNA水平解离的条件下维持核糖体组分的平衡合成中起重要作用。此外，观察到的β亚基信使RNA翻译效率的降低可能与RNA聚合酶组装中间体的积累所引起的抑制作用有关。
