Selfish gene leaves bacteria behind

A. York,  Nature Reviews Microbiology,  2021.

Mitochondrial genome evolution is characterized by functional streamlining and gene loss, and gain-of-function gene transfers into the mitochondrial genome are considered rare events. Milner, et al. identified a functional restriction modification (R-M) system in the mitochondrial genome of a marine protist that originated in bacteria. The type II R-M system was found in the mitochondrial genome of a marine heterotrophic katablepharid protist, and phylogenetic analyses suggest that the selfish genetic element consisting of an HpaII-like endonuclease and a cognate cytosine methyltransferase originated in bacteria within or related to Flavobacteriaceae. The authors showed that the R-M system is functional in both bacteria and yeast, and that a toxin–antitoxin relationship exists between the two proteins. The authors posit that the toxin–antitoxin function of the R-M system may have been co-opted to control biased or uniparental inheritance of mitochondria.


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