Himeno Hyouta, Nameki Nobukazu, Kurita Daisuke, Muto Akira, Abo Tatsuhiko
Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki 036-8561, Japan.
Division of Molecular Science, Graduate School of Science and Technology, Gunma University, 1-5-1, Tenjin-cho, Kiryu-shi, Gunma 376-8515, Japan.
Biochimie. 2015 Jul;114:102-12. doi: 10.1016/j.biochi.2014.11.014. Epub 2014 Nov 28.
Ribosomes often stall during protein synthesis in various situations in a cell, either unexpectedly or in a programmed fashion. While some of them remain stalled for gene regulation, many are rescued by some cellular systems. Ribosomes stalled at the 3' end of a truncated mRNA lacking a stop codon (non-stop mRNA) are rescued by trans-translation mediated by tmRNA (transfer-messenger RNA) and a partner protein, SmpB. Through trans-translation, a degradation tag is added to the C-termini of truncated polypeptides from a truncated mRNA to prevent them from accumulation in the cell. Trans-translation has crucial roles in a wide variety of cellular events, especially under stressful conditions. The trans-translation system is thought to be universally present in the bacterial domain, although it is not necessarily essential in all bacterial cells. It has recently been revealed that two other systems, one involving a small protein, ArfA, with RF2 and the other involving YaeJ (ArfB), a class I release factor homologue, operate to relieve ribosome stalling in Escherichia coli. Thus, many bacterial species would have multiple systems to cope with various kinds of stalled translation events.
在细胞内的各种情况下，核糖体在蛋白质合成过程中常常会停滞，这种停滞可能是意外发生的，也可能是程序性的。虽然其中一些核糖体因基因调控而持续停滞，但许多会被一些细胞系统拯救。在缺乏终止密码子的截短mRNA（无义mRNA）的3'末端停滞的核糖体，会通过由转移信使RNA（tmRNA）和伴侣蛋白SmpB介导的反式翻译来拯救。通过反式翻译，一个降解标签会被添加到来自截短mRNA的截短多肽的C末端，以防止它们在细胞内积累。反式翻译在各种各样的细胞事件中都起着关键作用，尤其是在应激条件下。虽然反式翻译系统并非在所有细菌细胞中都是必需的，但普遍存在于细菌域中。最近有研究表明，另外两个系统也能在大肠杆菌中发挥作用以缓解核糖体停滞，一个系统涉及一种小蛋白ArfA与RF2，另一个系统涉及I类释放因子同源物YaeJ（ArfB）。因此，许多细菌物种可能有多种系统来应对各种类型的翻译停滞事件。
