Restriction–modification (R–M) systems are commonly used by bacteria to defend against invading DNA. In these systems, a methyltransferase methylates endogenous DNA as a marker of 'self' and a cognate restriction enzyme cleaves invading DNA that lacks this modification. Guet and colleagues asked whether R–M systems ever err in the discrimination between self and non-self DNA, and whether such an error would incur a fitness cost. Testing the EcoRI and EcoRV R–M systems in Escherichia coli, they found that EcoRI, but not EcoRV, measurably, and stochastically, targets self DNA, albeit at a low frequency. The difference between EcoRI and EcoRV was attributed to a more efficient restriction enzyme, which makes for a more potent defence against foreign DNA but also increases the chance of cleaving self DNA prior to modification. However, fitness costs were minimal; E. coli cells growing at steady-state efficiently repaired EcoRI-mediated DNA damage and the induced SOS response was transient and did not affect cell viability.
References
Pleška, M. et al. Bacterial autoimmunity due to a restriction-modification system. Curr. Biol. http://dx.doi.org/10.1016/j.cub.2015.12.041 (2016)
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Attar, N. Damage limitation after friendly fire. Nat Rev Microbiol 14, 130 (2016). https://doi.org/10.1038/nrmicro.2016.20
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DOI: https://doi.org/10.1038/nrmicro.2016.20