Evolution of restriction-modification systems with one restriction endonuclease and two DNA methyltransferases

Abstract

Some restriction-modification systems contain two DNA methyltransferases. In the present work, we have classified such systems according to the families of catalytic domains present in restriction endonucleases and both DNA methyltransferases. The evolution of restriction-modification systems of one class was studied in detail. Systems in this class include an endonuclease with a NOV_C family domain and two DNA methyltransferases, both with DNA_methylase family domains. The phylogenetic tree of DNA methyltransferases from systems of this class consists of two clades of the same size. Two DNA methyltransferases of each restriction-modification system of the class belong to different clades. This indicates independent evolution of the two methyltransferases. We detected multiple cross-species horizontal transfers of systems as a whole, as well as cases of gene transfer between systems.