Bisulfite-free, Base-resolution, and Quantitative Sequencing of Cytosine Modifications

The deamination of unmodified cytosine to uracil by treatment with bisulfite has for decades been the gold standard for sequencing epigenetic DNA modifications including 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC). However, this harsh chemical reaction degrades the majority of the DNA and generates sequencing libraries with low complexity. Here, we present a novel bisulfite-free and base-resolution sequencing method, TET Assisted Pic-borane Sequencing (TAPS), for detection of 5mC and 5hmC. TAPS relies on mild reactions, detects modifications directly without affecting unmodified cytosines and can be adopted to detect other cytosine modifications. Compared with bisulfite sequencing, TAPS results in higher mapping rates, more even coverage and lower sequencing costs, enabling higher quality, more comprehensive and cheaper methylome analyses. One Sentence Summary A bisulfite-free and base-resolution method to directly sequence epigenetically modified cytosine.