IDENTIFYING RNA EDITING IN BACTERIAL mRNA IN THE CONTEXT OF TOXIN-ANTITOXIN SYSTEM

RNA editing, the process of converting one nucleotide type into another, is a widespread phenomenon in eukaryotes and when occurring in the context of mRNAs it has the potential to alter proteins sequence. The most common editing type is the conversion of Adenosine (A) to inosine (I) in the RNA molecule. However, unlike eukaryotes, in prokaryotes such editing events in mRNA were never reported. By sequencing both RNA and DNA samples from E.coli cultures, we have shown for the first time that A to I editing occurs on bacterial mRNA, and identified 15 new editing sites. Furthermore, we were able to identify the enzyme responsible for this editing activity. Strikingly, all editing events identified in mRNA are predicted to convert a Tyr codon into a Cys thus likely to affect protein sequence. Surprisingly, four out of the newly identified editing sites are located within the coding region of self-killing toxins that belong to the evolutionarily conserved hok family of toxin-antitoxin module. Focusing on one such toxin- HokB, we were able to show that editing levels are physiologically regulated during culture growth. In addition, our work reveals that editing increases HokB toxicity uncovering a new role of editing in bacteria - regulating proteins activity. By analyzing publically available deep sequencing data, we found that hokB editing is not unique to E.coli and can be found in additional pathogenic bacteria. HokB toxin was shown to depolarize the cell membrane, reduce the membranal proton-motive force and by that to mediate persistence and antibiotic tolerance. An intriguing possibility emerging from this work, that requires further study, is that hokB editing can further tune persistence and antibiotic tolerance in bacteria.