Nakano H, Goto S, Nakayashiki T, Inokuchi H
Department of Biophysics, Graduate School of Science, Kyoto University, Japan.
Mol Genet Genomics. 2001 Jun;265(4):615-21. doi: 10.1007/s004380100453.
An Escherichia coli strain with a deletion in the ssrA gene that encodes 10Sa RNA (tmRNA) was used to screen for temperature-sensitive (ts) mutants whose ts phenotypes were suppressible by introduction of the wild-type ssrA gene. Mutants in four different genes were isolated. Ts mutants of this type were also obtained in a screen for mutations in thyA, the structural gene for thymidylate synthase. The ThyA activity in crude extracts prepared from the ts mutants was temperature-sensitive. The presence of the ssrA gene caused an increase in the total amount of the temperature-sensitive enzyme expressed, rather than suppressing the ts activity of the enzyme itself. SsrA-DD, a mutant form of 10Sa RNA, suppressed the ts phenotype of a thyA mutant, suggesting that degradation of a tagged peptide was not required for suppression of the ts phenotype. Considering the fact that ssrA-suppressible mutants could be isolated as temperature-sensitive mutants with mutations in different genes, it seems evident that trans-translation can occur on mRNA that is not lacking its stop codon.
利用一株编码10Sa RNA（tmRNA）的ssrA基因缺失的大肠杆菌菌株，筛选温度敏感（ts）突变体，这些ts表型可通过导入野生型ssrA基因来抑制。分离出了四个不同基因中的突变体。在胸苷酸合成酶结构基因thyA的突变筛选中也获得了这种类型的ts突变体。从ts突变体制备的粗提物中的ThyA活性对温度敏感。ssrA基因的存在导致表达的温度敏感酶总量增加，而不是抑制该酶本身的ts活性。10Sa RNA的突变形式SsrA-DD抑制了thyA突变体的ts表型，这表明抑制ts表型不需要降解标记肽。考虑到可以将ssrA可抑制突变体分离为不同基因发生突变的温度敏感突变体，很明显反式翻译可以在不缺少终止密码子的mRNA上发生。
