Divergently overlapping cis-encoded antisense RNA regulating toxin-antitoxin systems from E. coli

Abstract

Toxin-antitoxin (TA) systems are categorized into three classes based on the type of antitoxin. In type I TA systems, the antitoxin is a small antisense RNA that inhibits translation of small toxic proteins by binding to the corresponding mRNAs. Those type I TA systems were originally identified as plasmid stabilization modules rendering a post-segregational killing (PSK) effect on the host cells. The type I TA loci also exist on the Escherichia coli chromosome but their biological functions are less clear. Genetic organization and regulatory elements of hok/sok and ldr/rdl families are very similar and the toxins are predicted to contain a transmembrane domain, but otherwise share no detectable sequence similarity. This review will give an overview of the type I TA modules of E. coli K-12, especially hok/sok, ldr/rdl and SOS-inducible symE/symR systems, which are regulated by divergently overlapping cis-encoded antisense RNAs.

Keywords: :

• small RNA
• noncoding RNA
• small protein
• post-transcriptional regulation
• SOS response
• repetitive sequence

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

The author is very much grateful to Gisela Storz for her comments on the manuscript and stimulating discussions to the symE/symR project, and Kenn Gerdes for his improvement on the manuscript and pioneering studies to the hok/sok system. The author also thanks Mori Hirotada for his encouragement to the LDR project and pleasant Sake meeting.