A novel immunity system for bacterial nucleic acid degrading toxins and its recruitment in various eukaryotic and DNA viral systems

Zhang, Dapeng; Iyer, Lakshminarayan M.; Aravind, L.

Nuclease toxins of the cytotoxic RNase fold. The last family of nucleases that we found encoded by genes linked to the SUKH superfamily genes was the cytotoxic RNase family (63) . This nuclease domain was first characterized as the toxin domain of the colicins E3 and E6 and is typified by a conserved active site configuration with an aspartate followed by a glutamate sandwiched between two histidines (Supplementary Data). The version of this domain in colicin E3 has been demonstrated to function as an EndoRNAse that specifically cleaves the phosphoester bond between bases 1493 and 1494 of 16S ribosomal RNA (63) . Given that versions detected in systems characterized in our current study are closely related to the version found in colicin E3 and E6, we posit that these nuclease domains act as RNAses that similarly cleave RNA in the target cells.