DNMT1 Caught in the Act

摘要

In eukaryotes, methylation of DNA, generally on the C base of CpG dinucleotides, is critical for the epigenetic regulation of numerous critical cellular processes. Patterns of DNA methylation are preserved from generation to generation, in large part by DNA methyltrans-ferase-1 (DNMT1) or in one of its homologs. Song et al. (p. 1036, published online 16 December; see the Perspective by Godley and Mondragon) have solved the structure of DNMT1 from mouse and humans, both free and bound to CpG-containing double-stranded DNA. The structure reveals how DNMT-1 avoids methylating sites that have unmethylated CpGs on both DNA strands, rather than the preferred target in which CpGs are methylated on one strand (the parental DNA) but not the other (the daughter DNA).