Bisulfite Modifications

This method looks for methylated cytosines across the DNA. Cytosines in both strands of DNA can be methylated when the strands are separated, bisulfite changes the non-methylated cytosines to uracil. Methyl groups protect methylated cytosines, protecting them from the conversion to uracil. Treatment of genomic DNA with sodium bisulfite results in the deamination of unmethylated cytosines to uracil. Leaving methylated cytosines intact allows 5-methylcytosines (5mCs) to be distinguished from unmethylated cytosines throughout the genomic DNA. Genomic DNA is treated with bisulfite followed by PCR amplification, cloning, and sequencing of individual PCR amplimers.

Many epigenetic questions can be addressed by the information of the methylated state on DNA molecules. DNA methylation plays an important role in understanding the development and progression of tumorigenesis by epigenetic modification and silencing of genes.

Note: The CpG locations are underlined in red while the non-CPG cytosine locations are in blue. BISUL_METH_FW, BISUL_METH_RC, BISUL_UNMETH_FW, and BISUL_UNMETH_RC are the sequence identifiers in the database.¹⁴