PT  - JOURNAL ARTICLE
AU  - Milner, David S.
AU  - Wideman, Jeremy G.
AU  - Stairs, Courtney W.
AU  - Dunn, Cory D.
AU  - Richards, Thomas A.
TI  - A functional bacterial-derived restriction modification system in the mitochondrion of a heterotrophic protist
AID  - 10.1101/2021.02.01.429123
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.01.429123
4099  - http://biorxiv.org/content/early/2021/02/01/2021.02.01.429123.short
4100  - http://biorxiv.org/content/early/2021/02/01/2021.02.01.429123.full
AB  - The overarching trend in mitochondrial evolution is functional streamlining coupled with gene loss; therefore, gene acquisition by mitochondria is considered to be exceedingly rare. Selfish elements in the form of self-splicing introns occur in many organellar genomes, but the wider diversity of selfish elements, and how they persist in organellar genomes, has not been explored. In the mitochondrial genome of a marine heterotrophic katablepharid protist, we identify a functional type II restriction modification system originating from a horizontal gene transfer event involving bacteria related to flavobacteria. This restriction modification system consists of an HpaII-like endonuclease and a cognate cytosine methyltransferase. We demonstrate that these proteins are functional by heterologous expression in both bacterial and eukaryotic cells. These results suggest that toxin-antitoxin selfish elements, such as restriction modification systems, could be co-opted by eukaryotic genomes to drive uniparental organellar inheritance.