Schifano Jason M, Cruz Jonathan W, Vvedenskaya Irina O, Edifor Regina, Ouyang Ming, Husson Robert N, Nickels Bryce E, Woychik Nancy A
Department of Biochemistry and Molecular Biology, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ, USA.
Waksman Institute, Rutgers University, Piscataway, NJ, USA Department of Genetics, Rutgers University, Piscataway, NJ, USA.
Nucleic Acids Res. 2016 Feb 18;44(3):1256-70. doi: 10.1093/nar/gkv1370. Epub 2016 Jan 5.
Toxin-antitoxin (TA) systems play key roles in bacterial persistence, biofilm formation and stress responses. The MazF toxin from the Escherichia coli mazEF TA system is a sequence- and single-strand-specific endoribonuclease, and many studies have led to the proposal that MazF family members exclusively target mRNA. However, recent data indicate some MazF toxins can cleave specific sites within rRNA in concert with mRNA. In this report, we identified the repertoire of RNAs cleaved by Mycobacterium tuberculosis toxin MazF-mt9 using an RNA-seq-based approach. This analysis revealed that two tRNAs were the principal targets of MazF-mt9, and each was cleaved at a single site in either the tRNA(Pro14) D-loop or within the tRNA(Lys43) anticodon. This highly selective target discrimination occurs through recognition of not only sequence but also structural determinants. Thus, MazF-mt9 represents the only MazF family member known to target tRNA and to require RNA structure for recognition and cleavage. Interestingly, the tRNase activity of MazF-mt9 mirrors basic features of eukaryotic tRNases that also generate stable tRNA-derived fragments that can inhibit translation in response to stress. Our data also suggest a role for tRNA distinct from its canonical adapter function in translation, as cleavage of tRNAs by MazF-mt9 downregulates bacterial growth.
毒素-抗毒素（TA）系统在细菌的持留性、生物膜形成和应激反应中发挥关键作用。大肠杆菌mazEF TA系统中的MazF毒素是一种序列和单链特异性内切核糖核酸酶，许多研究表明，MazF家族成员仅靶向mRNA。然而，最近的数据表明，一些MazF毒素可以与mRNA协同切割rRNA内的特定位点。在本报告中，我们使用基于RNA测序的方法鉴定了结核分枝杆菌毒素MazF-mt9切割的RNA种类。该分析表明，两种tRNA是MazF-mt9的主要靶标，每种tRNA在tRNA(Pro14) D环或tRNA(Lys43)反密码子内的单个位点被切割。这种高度选择性的靶标识别不仅通过序列识别，还通过结构决定因素来实现。因此，MazF-mt9是已知的唯一靶向tRNA并需要RNA结构进行识别和切割的MazF家族成员。有趣的是，MazF-mt9的tRNase活性反映了真核tRNase的基本特征，真核tRNase也能产生稳定的tRNA衍生片段，在应激时抑制翻译。我们的数据还表明，tRNA在翻译中的作用与其经典的衔接子功能不同，因为MazF-mt9对tRNA的切割会下调细菌的生长。
