Yoshida Hideji, Ueta Masami, Maki Yasushi, Sakai Akiko, Wada Akira
Department of Physics, Osaka Medical College, Takatsuki, Japan.
Genes Cells. 2009 Feb;14(2):271-80. doi: 10.1111/j.1365-2443.2008.01272.x. Epub 2008 Jan 15.
The canonical ribosome cycle in bacteria consists of initiation, elongation, termination, and recycling stages. After the recycling stage, initiation factor 3 (IF3) stabilizes ribosomal dissociation by binding to 30S subunits for the next round of translation. On the other hand, during the stationary growth phase, it has been elucidated that Escherichia coli ribosomes are dimerized (100S ribosome formation) by binding ribosome modulation factor (RMF) and hibernation promoting factor (HPF), leading to a hibernation stage. This indicates that 100S ribosomes are formed after these factors are scrambled for ribosomes concomitantly with transition from the log phase to the stationary phase. In this study, to elucidate the ribosomal events before 100S ribosome formation, the relationships between protein factors (RMF and HPF) involved in 100S ribosome formation and IF3 involved in initiation complex formation were examined. As a result of in vitro assays, it was found that ribosomal dissociation activity by IF3 fell, and that ribosomal dimerization activity by RMF and HPF was elevated more when using stationary-phase ribosomes than when using log-phase ribosomes. This suggests that ribosomes change into forms which are hard to bind with IF3 and easy to form 100S ribosomes by RMF and HPF concomitantly with transition from the log phase to the stationary phase.
细菌中的经典核糖体循环包括起始、延伸、终止和再循环阶段。在再循环阶段之后，起始因子3（IF3）通过与30S亚基结合来稳定核糖体解离，以便进行下一轮翻译。另一方面，在稳定生长期，已经阐明大肠杆菌核糖体通过结合核糖体调控因子（RMF）和休眠促进因子（HPF）而二聚化（形成100S核糖体），从而进入休眠阶段。这表明在这些因子与核糖体结合后，随着从对数期到稳定期的转变，100S核糖体形成。在本研究中，为了阐明100S核糖体形成之前的核糖体事件，研究了参与100S核糖体形成的蛋白质因子（RMF和HPF）与参与起始复合物形成的IF3之间的关系。体外实验结果发现，与使用对数期核糖体相比，使用稳定期核糖体时，IF3的核糖体解离活性下降，而RMF和HPF的核糖体二聚化活性升高。这表明随着从对数期到稳定期的转变，核糖体转变为难以与IF3结合且易于通过RMF和HPF形成100S核糖体的形式。
