DNA-methylation patterns are important for regulating genome functions, and
are determined by the enzymatic processes of methylation and demethylation
. The demethylating enzyme has now been identified: a mammalian complementa
ry DNA encodes a methyl-CpG-binding domain, bears a demethylase activity th
at transforms methylated cytosine bases to cytosine, and demethylates a pla
smid when the cDNA is translated or transiently transfected into human embr
yonal kidney cells in vitro. The discovery of this DNA demethylase should p
rovide a basis for the molecular and developmental analysis of the role of
DNA methylation and demethylation.