Asato Yukio
University of Massachusetts Dartmouth, N Dartmouth, Massachusetts 02747, USA.
Curr Issues Mol Biol. 2005 Jan;7(1):109-17.
The regulation of ribosome synthesis has been investigated for nearly five decades. In earlier studies, the control of rRNA synthesis in bacteria was found to be dependent on nutrient composition of the growth media or cell growth rates, and these observations led to the growth rate-dependent regulation model. Also developed were stringent control, feedback ribosome synthesis, passive regulation, and antitermination models. Current evidence indicates that upstream (UP) element, molecular effectors, ppGpp and iNTP (initiating nucleoside triphosphate), and trans-acting proteins, Fis and H-NS, play important roles in the control of rRNA synthesis in response to changing nutritional environments. The mechanisms for the ribosome feedback regulation, and growth rate-dependent controls of rRNA synthesis remain to be determined despite numerous investigations. r-protein synthesis can be controlled by translational coupling, translation repression, or premature transcription termination. In Synechococcus, a photoautotroph, ribosome synthesis occurs early in the cell cycle as programmed events under conditions that support balanced growth. Periods of r-protein synthesis occur before rRNA synthesis periods, and rRNA synthesis is stimulated by a light-activated gene regulatory protein. These observations suggest that gene regulatory proteins are involved in the coordinate regulation of ribosome assembly in Synechococcus.
核糖体合成的调控已被研究了近五十年。在早期研究中，发现细菌中rRNA合成的控制取决于生长培养基的营养成分或细胞生长速率，这些观察结果导致了生长速率依赖性调控模型的提出。同时还发展出了严格控制、反馈核糖体合成、被动调控和抗终止模型。目前的证据表明，上游（UP）元件、分子效应物、ppGpp和iNTP（起始核苷三磷酸）以及反式作用蛋白Fis和H-NS在响应不断变化的营养环境时对rRNA合成的控制中发挥着重要作用。尽管进行了大量研究，但核糖体反馈调控以及rRNA合成的生长速率依赖性控制机制仍有待确定。r蛋白合成可通过翻译偶联、翻译抑制或转录提前终止来控制。在光合自养生物集胞藻中，在支持平衡生长的条件下，核糖体合成作为程序性事件在细胞周期早期发生。r蛋白合成期先于rRNA合成期出现，并且rRNA合成受到光激活基因调控蛋白的刺激。这些观察结果表明，基因调控蛋白参与了集胞藻中核糖体组装的协调调控。
