DNA methylation proteins, such as DNA methyltransferases DNMT1, DNMT3A, and DNMT3B, are useful for the study of enzyme kinetics, screening inhibitors, and selectivity profiling related to DNA methylation. DNA methylation is defined as the addition of a methyl group to the 5-carbon position of cytosine. It is implicated in numerous biological processes and if not regulated properly, can result in the development of diseases, especially cancer.