Abstract
Here we identified a functional MazEF-dr system in the exceptionally stress-resistant bacterium D. radiodurans. We showed that overexpression of the toxin MazF-dr inhibited the growth of Escherichia coli. The toxic effect of MazF-dr was due to its sequence-specific endoribonuclease activity on RNAs containing a consensus 5′ACA3′, and it could be neutralized by MazE-dr. The MazF-dr showed a special cleavage preference for the nucleotide present before the ACA sequence with the order by U>A>G>C. MazEF-dr mediated the death of D. radiodurans cells under sub-lethal dose of stresses. The characteristics of programmed cell death (PCD) including membrane blebbing, loss of membrane integrity and cytoplasm condensation occurred in a fraction of the wild-type population at sub-lethal concentration of the DNA damaging agent mitomycin C (MMC); however, a MazEF-dr mutation relieved the cell death, suggesting that MazEF-dr mediated cell death through its endoribonuclease activity in response to DNA damage stress. The MazEF-dr-mediated cell death of a fraction of the population might serve as a survival strategy for the remaining population of D. radiodurans under DNA damage stress.
Highlights
Toxin–antitoxin (TA) systems, referred to as addiction or suicide modules, are distributed widely in free-living organisms including bacteria and archaea (Pandey and Gerdes, 2005; Makarova et al, 2009)
Two pairs of putative MazEF-encoding genes were found in the D. radiodurans genome: dr0416-dr0417 and dr0661dr0662, which are consistent with the predicted sequences in the Toxin-Antitoxin Database (TADB) (Shao et al, 2011)
These results indicated that the dr0416-dr0417 locus may function as MazEF-type TA system and we refer to them as MazEF-dr for MazEF in D. radiodurans
Summary
Toxin–antitoxin (TA) systems, referred to as addiction or suicide modules, are distributed widely in free-living organisms including bacteria and archaea (Pandey and Gerdes, 2005; Makarova et al, 2009). Typical TA systems have two components that are co-transcribed from a bi-cistronic operon, in which the upstream gene encodes a labile antitoxin and the downstream gene encodes a stable toxin. TA systems are currently classified into at least three types: types I and III antitoxins are RNAs that either inhibit the expression or activity of the toxin, while the most widespread type II TA system contains a protein antitoxin. In type II TA systems, the antitoxin neutralizes the activity of the toxin via a physical interaction (Kamada et al, 2003). Once the concentration of the antitoxin decreases, the free toxin will act on its targets (RNAs or proteins), which results in bactericidal or bacteriostatic
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