Nitrosomonas europaea MazF Specifically Recognises the UGG Motif and Promotes Selective RNA Degradation.

Tatsuki Miyamoto,Satoshi Tsuneda,Naohiro Noda,Masako Tsuruga,Rie Aoi,Yuri Ota,Akiko Yokota

doi:10.3389/fmicb.2018.02386

Abstract

Toxin-antitoxin (TA) systems are implicated in prokaryotic stress adaptation. Previously, bioinformatics analysis predicted that such systems are abundant in some slowly growing chemolithotrophs; e.g., Nitrosomonas europaea. Nevertheless, the molecular functions of these stress-response modules remain largely unclear, limiting insight regarding their physiological roles. Herein, we show that one of the putative MazF family members, encoded at the ALW85_RS04820 locus, constitutes a functional toxin that engenders a TA pair with its cognate MazE antitoxin. The coordinate application of a specialised RNA-Seq and a fluorescence quenching technique clarified that a unique triplet, UGG, serves as the determinant for MazF cleavage. Notably, statistical analysis predicted that two transcripts, which are unique in the autotroph, comprise the prime targets of the MazF endoribonuclease: hydroxylamine dehydrogenase (hao), which is essential for ammonia oxidation, and a large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (rbcL), which plays an important role in carbon assimilation. Given that N. europaea obtains energy and reductants via ammonia oxidation and the carbon for its growth from carbon dioxide, the chemolithotroph might use the MazF endoribonuclease to modulate its translation profile and subsequent biochemical reactions.

Highlights

Toxin-antitoxin (TA) systems comprise small genetic modules that modulate microbial cell fates in stressful environments
These results suggest that MazEFne1 constitutes a TA system
A propitious strategy to survive in fluctuating surroundings is to regulate growth, with prokaryotic TA systems being a well-known example of such a strategy (Hall et al, 2017)

Summary

Introduction

Toxin-antitoxin (TA) systems comprise small genetic modules that modulate microbial cell fates in stressful environments. During periods of low or no stress, antitoxins potently inactivate toxins, allowing microbes to grow normally. Antitoxins are preferentially degraded, resulting in toxin activation and subsequent microbial growth arrest (Schuster and Bertram, 2013). These systems are grouped into six distinct classes depending on antitoxin features (Page and Peti, 2016; Hall et al, 2017). In other TA systems, the antitoxins consist of proteins that counteract the toxins by forming a TA protein complex (type II) (Gerdes et al, 2005), functioning as an antagonist

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Results

Conclusion