Identification of methylated deoxyadenosines in vertebrates reveals diversity in DNA modifications

Methylation of cytosine deoxynucleotides (dC(5m)) is a well-established epigenetic mark, but in higher eukaryotes much less is known about modifications affecting other deoxynucleotides. Here, we report the detection of N-6-methyl-deoxyadenosine (dA(6m)) in vertebrate DNA, specifically in Xenopus laevis, but also in other species including mouse and human. Our methylome analysis reveals that dA(6m) is widely distributed across the eukaryotic genome, is present in different cell types, but commonly depleted from gene exons. Thus, direct DNA modifications might be more widespread than previously thought.