Oxidative Bisulfite Sequencing: An Experimental and Computational Protocol.

Bisulfite sequencing (BS-seq) remains the gold standard technique to quantitively map DNA methylation at a single-base resolution. However, BS-seq cannot discriminate between 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC). Oxidative bisulfite sequencing (oxBS-seq) was one of the first techniques that enabled absolute quantification of 5mC and 5hmC at single-base resolution. OxBS-seq uses chemical oxidation of 5hmC prior to bisulfite treatment to provide a direct readout of 5mC; comparison with BS-seq data can then be used to infer 5hmC levels. Here we describe in detail an updated version of our laboratory's oxBS-seq protocol, which uses potassium perruthenate (KRuO4) as an oxidant. We also describe a bioinformatics pipeline designed to handle Illumina short read sequencing data from whole-genome oxBS-seq.