Step I: DNA Glucosylation Reaction with T4 β-glucosyltransferase (T4-BGT) Genomic DNA of interest is treated with T4-BGT, adding a glucose moeity to 5-hydroxymethylcytosine. This reaction is sequence-independent - therefore all 5-hmC will be glucosylated, unmodified or 5-mC containing DNA will not be
Step II: Restriction Endonuclease Digestion
MspI and HpaII recognize the same sequence (CCGG) but are sensitive to different methylation status. HpaII cleaves only a completely unmodified site: any modification (5-mC, 5-hmC or 5-ghmC) at either cytosine blocks cleavage. MspI will recognize and cleave 5-mC and 5-hmC, but not 5-ghmC.
Step III: Interrogation of the Locus by PCR as little as 20 ng of input DNA can be used. Amplification of the experimental (glucosylated and digested) and control (mock glucosylated and digested) target DNA with primers flanking a CCGG site of interest (100–200 bp) is performed. If the CpG site contains 5-hydroxymethylcytosine, a band is detected after glucosylation and digestion, but not in the non-glucosylated control reaction (see Figure 2). Real time PCR will give an approximation of how much hydroxymethylcytosine is in this particular site.