DNA adenine methylation of GATC sequences appeared recently in the Escherichia coli lineage

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Abstract
The presence of methylated adenine at GATC sequences (Dam phenotype) were examined in the DNA of 23 eubacteria and 13 archaebacteria by using isoshizomer restriction enzymes. A completely Dam+ phenotype was found in bacteria of 9 genera related to the families Enterobacteriaceae, Parvbacteriaceae and Vibrionaceae, and in the 5 cyanobacteria tested. A partial Dam+ phenotype was found in the 2 archaebacteria Halobacterium saccharovorum and Methanobacterium sp. strain Ivanov. All of the other archaebacteria (3 genera) and eubacteria (9 genera) tested were Dam-. Phylogenetic analysis, based on the evolutionary tree of Fox et al., indicates that dam methylation in the Escherichia coli lineage appeared recently in bacterial evolution and is restricted to a small range of closely related bacteria.