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.


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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / metabolism*
  • Protein Biosynthesis / physiology
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Ribosomal, 23S / genetics
  • RNA, Ribosomal, 23S / metabolism*
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism*
  • Ribosome Subunits, Large, Bacterial / genetics
  • Ribosome Subunits, Large, Bacterial / metabolism*
  • Ribosome Subunits, Small, Bacterial / genetics
  • Ribosome Subunits, Small, Bacterial / metabolism*


  • Bacterial Proteins
  • RNA, Bacterial
  • RNA, Messenger
  • RNA, Ribosomal, 23S
  • RNA-Binding Proteins