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Mycobacterial toxin MazF-mt6 inhibits translation through cleavage of 23S rRNA at the ribosomal A site.

ABSTRACT: The Mycobacterium tuberculosis genome contains an unusually high number of toxin-antitoxin modules, some of which have been suggested to play a role in the establishment and maintenance of latent tuberculosis. Nine of these toxin-antitoxin loci belong to the mazEF family, encoding the intracellular toxin MazF and its antitoxin inhibitor MazE. Nearly every MazF ortholog recognizes a unique three- or five-base RNA sequence and cleaves mRNA. As a result, these toxins selectively target a subset of the transcriptome for degradation and are known as "mRNA interferases." Here we demonstrate that a MazF family member from M. tuberculosis, MazF-mt6, has an additional role--inhibiting translation through targeted cleavage of 23S rRNA in the evolutionarily conserved helix/loop 70. We first determined that MazF-mt6 cleaves mRNA at (5')UU?CCU(3') sequences. We then discovered that MazF-mt6 also cleaves M. tuberculosis 23S rRNA at a single UUCCU in the ribosomal A site that contacts tRNA and ribosome recycling factor. To gain further mechanistic insight, we demonstrated that MazF-mt6-mediated cleavage of rRNA can inhibit protein synthesis in the absence of mRNA cleavage. Finally, consistent with the position of 23S rRNA cleavage, MazF-mt6 destabilized 50S-30S ribosomal subunit association. Collectively, these results show that MazF toxins do not universally act as mRNA interferases, because MazF-mt6 inhibits protein synthesis by cleaving 23S rRNA in the ribosome active center.

SUBMITTER: Schifano JM

PROVIDER: S-EPMC3666664 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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Mycobacterial toxin MazF-mt6 inhibits translation through cleavage of 23S rRNA at the ribosomal A site.

Schifano Jason M JM Edifor Regina R Sharp Jared D JD Ouyang Ming M Konkimalla Arvind A Husson Robert N RN Woychik Nancy A NA

Proceedings of the National Academy of Sciences of the United States of America 20130506 21

The Mycobacterium tuberculosis genome contains an unusually high number of toxin-antitoxin modules, some of which have been suggested to play a role in the establishment and maintenance of latent tuberculosis. Nine of these toxin-antitoxin loci belong to the mazEF family, encoding the intracellular toxin MazF and its antitoxin inhibitor MazE. Nearly every MazF ortholog recognizes a unique three- or five-base RNA sequence and cleaves mRNA. As a result, these toxins selectively target a subset of ...[more]

PMID: 23650345

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Project description:Bacterial toxin-antitoxin systems help bacteria to reduce their metabolism in various stressful conditions and also play a part in generating antibiotic tolerant bacterial subpopulation called persisters. Many toxins of the bacterial toxin-antitoxin systems are ribonucleases. Such toxins have been mostly viewed as degraders of mRNA, however recently it was demonstrated that they are also capable of cleaving non-coding RNA. Current libraries are a part of a project which aims to identify the major RNA cleavage sites (in mRNA, rRNA and regulatory non-coding RNA) of MazF and MqsR toxins in E. coli. We were also interested in the activity of promoters during toxin overexpression. We used a targeted RNA-sequencing approach that allowed us to map the distinct 5- and 3-ends of toxin-cleaved RNA and also the beginnings of transcripts. We extracted total RNA from cultures where the expression of MazF or MqsR was induced; RNA from log phase culture was used as the control. In addition, RNA extracted from stationary phase culture was used to test for the possible toxin cleavage in natural stress conditions. The cleaved RNA is rapidly recycled making it possible that we miss important cleavage sites due to RNA degradation during the prolonged stationary phase. Therefore, in addition to wt E. coli we also used stationary phase RNA from exoribonuclease deficient strain where RNA cleavage products accumulate. Identification of the 5 ends is based on ligation of RNA adapters to the cellular RNA molecules, which requires 5 -monophosphates. Mapping of the 3 -ends is based on poly(A) tailing of RNA, which requires 3 -OH groups. Transcription initiation, ordinary cellular RNases, and toxin endonucleases all produce different types of RNA ends. These can be enzymatically converted to 5 -phosphates and 3 -OHs, which allows one to separately quantify the RNA ends produced by each of these processes from a single biological sample. Briefly, (i) primary transcripts have 5 -triphosphate ends that can be converted to monophosphate by Tobacco Acid Pyrophosphatase (TAP), and 3 -hydroxyl ends that can be directly polyadenylated by poly(A) polymerase. (ii) Most cellular RNases (excluding RNase I and the toxins) produce 5 -monophosphates and 3 -hydroxyls, which are directly usable for ligation/polyadenylation. (iii) RNase I, MazF, and several other toxins produce 5 -hydroxyl ends that need to be phosphorylated by T4 Polynucleotide Kinase (PNK) prior to ligation, and 2,3 -cyclic phosphates that need to be dephosphorylated and converted to 3 -hydroxyls, also by T4 PNK. In short, for each of our RNA samples three 5 end and two 3 end libraries were made. The PNK treated libraries contain reads mapping specifically to 5- or 3-ends left by toxin (or RNaseI) cleavage and TAP treated libraries have extra reads mapping to beginnings of the transcripts.

Dataset Information

Mycobacterial toxin MazF-mt6 inhibits translation through cleavage of 23S rRNA at the ribosomal A site.

Publications

Mycobacterial toxin MazF-mt6 inhibits translation through cleavage of 23S rRNA at the ribosomal A site.

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