Figure 3.

Maintenance and erasure of DNA methylation marks in normal cells. DNA methylation patterns are transmitted during DNA replication, where DNMT1 maintains global DNA methylation, whereas de novo methylation is performed by DNMT3A and DNMT3B proteins in complex with DNMT3L (not shown), a closely related homolog lacking a catalytic domain. DNA methylation marks can be deleted through a molecular mechanism in the absence of functional DNA methylation maintenance machinery during successive rounds of replication. On the contrary, the active demethylation of DNA occurs through an enzymatic process that eliminates or modifies the methyl group of 5 mC by the action of enzymes referred to as ten-eleven translocation (TET) enzymes.