Modified Nucleotides for Discrimination between Cytosine and the Epigenetic Marker 5-Methylcytosine

5-Methyl-2'-deoxycytosine, the most common epigenetic marker of DNA in eukaryotic cells, plays a key role in gene regulation and affects various cellular processes such as development and carcinogenesis. Therefore, the detection of 5mC can serve as an important biomarker for diagnostics. Here we describe that modified dGTP analogues as well as modified primers are able to sense the presence or absence of a single methylation of C, even though this modification does not interfere directly with Watson-Crick nucleobase pairing. By screening several modified nucleotide scaffolds, O(6)-modified 2'-deoxyguanosine analogues were identified as discriminating between C and 5mC. These modified nucleotides might find application in site-specific 5mC detection, for example, through real-time PCR approaches.