Condon C, Squires C, Squires C L
Department of Molecular Biology and Microbiology, Tufts University Health Sciences Campus, Boston, Massachusetts 02111, USA.
Microbiol Rev. 1995 Dec;59(4):623-45. doi: 10.1128/mr.59.4.623-645.1995.
The control of rRNA synthesis in response to both extra- and intracellular signals has been a subject of interest to microbial physiologists for nearly four decades, beginning with the observations that Salmonella typhimurium cells grown on rich medium are larger and contain more RNA than those grown on poor medium. This was followed shortly by the discovery of the stringent response in Escherichia coli, which has continued to be the organism of choice for the study of rRNA synthesis. In this review, we summarize four general areas of E. coli rRNA transcription control: stringent control, growth rate regulation, upstream activation, and anti-termination. We also cite similar mechanisms in other bacteria and eukaryotes. The separation of growth rate-dependent control of rRNA synthesis from stringent control continues to be a subject of controversy. One model holds that the nucleotide ppGpp is the key effector for both mechanisms, while another school holds that it is unlikely that ppGpp or any other single effector is solely responsible for growth rate-dependent control. Recent studies on activation of rRNA synthesis by cis-acting upstream sequences has led to the discovery of a new class of promoters that make contact with RNA polymerase at a third position, called the UP element, in addition to the well-known -10 and -35 regions. Lastly, clues as to the role of antitermination in rRNA operons have begun to appear. Transcription complexes modified at the antiterminator site appear to elongate faster and are resistant to the inhibitory effects of ppGpp during the stringent response.
近四十年来，响应细胞外和细胞内信号对核糖体RNA（rRNA）合成进行控制一直是微生物生理学家感兴趣的课题，最初是观察到在丰富培养基上生长的鼠伤寒沙门氏菌细胞比在贫瘠培养基上生长的细胞更大且含有更多的RNA。此后不久，大肠杆菌中严格反应的发现随之而来，大肠杆菌一直是研究rRNA合成的首选生物体。在这篇综述中，我们总结了大肠杆菌rRNA转录控制的四个一般领域：严格控制、生长速率调节、上游激活和抗终止。我们还列举了其他细菌和真核生物中的类似机制。将rRNA合成的生长速率依赖性控制与严格控制区分开来仍然是一个有争议的话题。一种模型认为核苷酸鸟苷四磷酸（ppGpp）是这两种机制的关键效应物，而另一种学派则认为ppGpp或任何其他单一效应物不太可能单独负责生长速率依赖性控制。最近关于顺式作用上游序列激活rRNA合成的研究导致发现了一类新的启动子，除了众所周知的 -10和 -35区域外，它们在第三个位置与RNA聚合酶接触，称为上游元件（UP元件）。最后，关于抗终止在rRNA操纵子中的作用的线索已经开始出现。在抗终止位点修饰的转录复合物似乎延伸得更快，并且在严格反应期间对ppGpp的抑制作用具有抗性。
