PERSPECTIVES Phylogeny of Methylomes MOLECULAR BIOLOGY

The patterns of DNA methylation across the genomes of 20 eukaryotes reveal conserved features and specifi c roles during evolution. T he DNA of most species is methylated, containing the modifi ed base 5-meth-ylcytosine. This modification has a role in silencing gene expression, among other important functions ( 1, 2). Advances in sequencing methods have allowed mea-surement of the fi rst complete genome-wide DNA methylation map (“methylome”) of the model plant Arabidopsis thaliana and human cells ( 3 – 5). Studies by Feng et al. ( 6) and by Zemach et al. on page 916 of this issue ( 7