Baik Sarah, Inoue Koichi, Ouyang Ming, Inouye Masayori
Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
J Bacteriol. 2009 Oct;191(19):6157-66. doi: 10.1128/JB.00699-09. Epub 2009 Jul 24.
The toxin MazF in Escherichia coli cleaves single-stranded RNAs specifically at ACA sequences. MazF overexpression virtually eliminates all cellular mRNAs to completely block protein synthesis. However, protein synthesis can continue on an mRNA that is devoid of ACA triplets. The finding that ribosomal RNAs remain intact in the face of complete translation arrest suggested a purpose for such preservation. We therefore examined the sequences of all transcribed RNAs to determine if there was any statistically significant bias against ACA. While ACA motifs are absent from tmRNA, 4.5S RNA, and seven of the eight 5S rRNAs, statistical analysis revealed that only for tmRNA was the absence nonrandom. The introduction of single-strand ACAs makes tmRNA highly susceptible to MazF cleavage. Furthermore, analysis of tmRNA sequences from 442 bacteria showed that the discrimination against ACA in tmRNAs was seen mostly in enterobacteria. We propose that the unusual bias against ACA in tmRNA may have coevolved with the acquisition of MazF.
大肠杆菌中的毒素MazF专门在ACA序列处切割单链RNA。MazF的过表达几乎消除了所有细胞mRNA，从而完全阻断蛋白质合成。然而，在没有ACA三联体的mRNA上，蛋白质合成仍可继续。核糖体RNA在完全翻译停滞的情况下仍保持完整这一发现表明了这种保留的目的。因此，我们检查了所有转录RNA的序列，以确定是否存在对ACA的任何统计学上显著的偏好。虽然在转移信使RNA（tmRNA）、4.5S RNA和八个5S核糖体RNA中的七个中不存在ACA基序，但统计分析表明，只有tmRNA的缺失是非随机的。单链ACA的引入使tmRNA极易受到MazF切割的影响。此外，对442种细菌的tmRNA序列分析表明，对tmRNA中ACA的歧视主要出现在肠杆菌中。我们提出，tmRNA中对ACA的异常偏好可能与MazF的获得共同进化。
