Booth, M.J. et al. Nat. Chem. doi:10.1038/nchem.1893 (23 March 2014).

Cytosine methylation is a dynamic form of epigenetic regulation, and demethylation occurs via intermediates such as 5-formylcytosine (5-fC) that may themselves play regulatory roles. The position of methylated cytosines (5-mC) in the genome can be inferred using bisulfite to convert unmodified cytosine to thymine during sequencing (5-fC is also read as thymine in the process). Booth et al. have developed reduced bisulfite sequencing (redBS-Seq), which uses sodium borohydride to specifically reduce 5-fC and thereby protect it from bisulfite conversion. redBS-Seq provides single-base resolution and may be more efficient than the related fCABs-Seq (chemically assisted bisulfite sequencing) method, making the genome-wide discovery of this rare mark potentially more practical. Booth et al. sequenced 5-fC in addition to 5-mC and another intermediate in mouse embryonic stem cell genomes.