A complete understanding of the potential function of 5-hydroxymethylcytosine (5-hmC), a DNA cytosine modification in mammalian cells, requires an accurate single-base resolution sequencing method. Here we describe a modified bisulfite-sequencing method, Tet-assisted bisulfite sequencing (TAB-seq), which can identify 5-hmC at single-base resolution, as well as determine its abundance at each modification site. This protocol involves β-glucosyltransferase (β-GT)-mediated protection of 5-hmC (glucosylation) and recombinant mouse Tet1(mTet1)-mediated oxidation of 5-methylcytosine (5-mC) to 5-carboxylcytosine (5-caC). After the subsequent bisulfite treatment and PCR amplification, both cytosine and 5-caC (derived from 5-mC) are converted to thymine (T), whereas 5-hmC reads as C. The treated genomic DNA is suitable for both whole-genome and locus-specific sequencing. The entire procedure (which does not include data analysis) can be completed in 14 d for whole-genome sequencing or 7 d for locus-specific sequencing.
At a glance
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- Supplementary Note 1 (213K)
Sequence of 5hmC spike-in control
- Supplementary Note 2 (199K)
Insertion Sequence of mTet1. The mouse TET1 (1367-2039) gene with one flag tag was cloned into the insect cell expression plasmid pFastBac Dual (Invitrogen, cat. 10712-024). The restriction enzyme cutting sites are BssHII and NotI.