Active DNA demethylation is an important part of epigenetic regulation in plants and animals.In Arabidopsis, the ROS1/DME subfamily of DNA glycosylases function to promote DNA demethylation through a base excision-repair pathway.These specialized bifunctional DNA glycosylases remove the 5-methylcytosine base and then cleave the DNA backnone at the abasic site using either β3 elimination or β, δ elimination, resulting in a gap that is then filled with an unmethylated cytosine nucleotide by as yet unknown DNA polymerase and ligase enzymes.