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Toxins 2017, 9(1), 29; doi:10.3390/toxins9010029

RnlB Antitoxin of the Escherichia coli RnlA-RnlB Toxin–Antitoxin Module Requires RNase HI for Inhibition of RnlA Toxin Activity

Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
Department of Microbiology, School of Medicine, Dokkyo Medical University, 880 Kitakobayashi, Mibu-machi, Shimotsuga-gun, Tochigi 321-0293, Japan
Author to whom correspondence should be addressed.
Academic Editor: Shin-ichi Miyoshi
Received: 28 November 2016 / Revised: 28 December 2016 / Accepted: 5 January 2017 / Published: 11 January 2017
(This article belongs to the Section Bacterial Toxins)
View Full-Text   |   Download PDF [2233 KB, uploaded 11 January 2017]   |  


The Escherichia coli RnlA-RnlB toxin–antitoxin system is related to the anti-phage mechanism. Under normal growth conditions, an RnlA toxin with endoribonuclease activity is inhibited by binding of its cognate RnlB antitoxin. After bacteriophage T4 infection, RnlA is activated by the disappearance of RnlB, resulting in the rapid degradation of T4 mRNAs and consequently no T4 propagation when T4 dmd encoding a phage antitoxin against RnlA is defective. Intriguingly, E. coli RNase HI, which plays a key role in DNA replication, is required for the activation of RnlA and stimulates the RNA cleavage activity of RnlA. Here, we report an additional role of RNase HI in the regulation of RnlA-RnlB system. Both RNase HI and RnlB are associated with NRD (one of three domains of RnlA). The interaction between RnlB and NRD depends on RNase HI. Exogenous expression of RnlA in wild-type cells has no effect on cell growth because of endogenous RnlB and this inhibition of RnlA toxicity requires RNase HI and NRD. These results suggest that RNase HI recruits RnlB to RnlA through NRD for inhibiting RnlA toxicity and thus plays two contrary roles in the regulation of RnlA-RnlB system. View Full-Text
Keywords: toxin–antitoxin system; RnlA-RnlB; RNase HI; Escherichia coli; bacteriophage toxin–antitoxin system; RnlA-RnlB; RNase HI; Escherichia coli; bacteriophage

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Naka, K.; Qi, D.; Yonesaki, T.; Otsuka, Y. RnlB Antitoxin of the Escherichia coli RnlA-RnlB Toxin–Antitoxin Module Requires RNase HI for Inhibition of RnlA Toxin Activity. Toxins 2017, 9, 29.

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