The bacterial toxin RelE displays codon-specific cleavage of rnRNAs in the ribosomal A site

The Escherichia coli reIBE operon encodes a toxin-antitoxin pair, ReIE-ReIB. ReIB can reverse inhibition of protein synthesis by ReIE in vivo. We have found that although ReIE does not degrade free RNA, it cleaves mRNA in the ribosomal A site with high codon specificity. Among stop codons UAG is cleaved with fast, UAA intermediate and UGA slow rate, while UCG and CAG are cleaved most rapidly among sense codons. We suggest that inhibition of protein synthesis by ReIE is reversed with the help of tmRNA, and that ReIE plays a regulatory role in bacteria during adaptation to poor growth conditions.