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Published on: October 31, 2014
Toxins MazF and MqsR cleave Escherichia coli rRNA precursors at multiple sites
Toomas Mets1, Markus Lippus1, David Schryer1
1a Institute of Technology, University of Tartu , Tartu , Estonia.
Abstract:
The endoribonuclease toxins of the E. coli toxin-antitoxin systems arrest bacterial growth and protein synthesis by targeting cellular mRNAs. As an exception, E. coli MazF was reported to cleave also 16S rRNA at a single site and separate an anti-Shine-Dalgarno sequence-containing RNA fragment from the ribosome. We noticed extensive rRNA fragmentation in response to induction of the toxins MazF and MqsR, which suggested that these toxins can cleave rRNA at multiple sites. We adapted differential RNA-sequencing to map the toxin-cleaved 5'- and 3'-ends. Our results show that the MazF and MqsR cleavage sites are located within structured rRNA regions and, therefore, are not accessible in assembled ribosomes. Most of the rRNA fragments are located in the aberrant ribosomal subunits that accumulate in response to toxin induction and contain unprocessed rRNA precursors. We did not detect MazF- or MqsR-cleaved rRNA in stationary phase bacteria and in assembled ribosomes. Thus, we conclude that MazF and MqsR cleave rRNA precursors before the ribosomes are assembled and potentially facilitate the decay of surplus rRNA transcripts during stress.
Insights
Bacterial toxins MazF and MqsR cleave ribosomal RNA (rRNA) precursors, not mature ribosomes. This process, observed during stress, may help degrade excess rRNA transcripts.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Toxin-antitoxin systems are crucial for bacterial survival and stress response.
- Endoribonuclease toxins typically target messenger RNAs (mRNAs) to inhibit protein synthesis.
- E. coli MazF was previously known to cleave 16S ribosomal RNA (rRNA) at a specific site.
Purpose of the Study:
- To investigate the potential for MazF and MqsR toxins to cleave rRNA at multiple sites.
- To map the specific cleavage sites of MazF and MqsR on rRNA.
- To determine when rRNA cleavage by these toxins occurs in the bacterial lifecycle.
Main Methods:
- Differential RNA-sequencing (dRNA-seq) was employed to identify toxin-induced RNA cleavage sites.
- Analysis focused on mapping 5' and 3' ends of cleaved RNA fragments.
- Comparison of rRNA cleavage patterns in response to MazF and MqsR toxin induction.
Main Results:
- MazF and MqsR toxins induce extensive rRNA fragmentation.
- Cleavage sites are located in structured rRNA regions, inaccessible in assembled ribosomes.
- Fragments originate from aberrant ribosomal subunits containing unprocessed rRNA precursors.
Conclusions:
- MazF and MqsR cleave rRNA precursors prior to ribosome assembly.
- These toxins do not cleave rRNA in assembled ribosomes or during stationary phase.
- Toxin-mediated rRNA cleavage may facilitate the degradation of surplus rRNA during stress conditions.
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