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

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Schifano JM, Edifor R, Sharp JD, Ouyang M, Konkimalla A, Husson RN, Woychik NA

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

Proc Natl Acad Sci U S A. 2013 May 21;110(21):8501-6. doi: 10.1073/pnas.1222031110. Epub 2013 May 6.

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23650345 [ View in PubMed
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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 downward arrowCCU(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.

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