Bisulfite Modification of Cytosine and 5-Methylcytosine as used in Epigenetic Studies

Epigenetic changes are intimately linked to cancer and other human diseases. This science has been developed on the basis of chemical analysis of DNA methylation. In most of these studies, the data are obtained by use of bisulfite genomic sequencing. Bisulfite deaminates specifically cytosine residues in single-stranded DNA molecules. 5-Methylcytosine resists the action of bisulfite. This difference in bisulfite reaction constitutes the principle for the detection of methylated sites. This review examines the details of chemistry involved in the bisulfite modification of DNA; deamination steps, single strand specificity, and DNA degradation in relation to chain cleavage. Points of uncertainty in these processes are mentioned. Recent advances by use of a 10 M bisulfite solution are explained, and a convenient laboratory protocol for quantifying bisulfite is described.