5-Hydroxymethylcytosine is a modified base found in the DNA of T-even bacteriophages (T2, T4, T6) (see here). Most of the 5-hydroxymethylcytosine residues in these viruses are in the form of -glucosyl-5-hydroxymethylcytosine (i.e., their hydroxymethyl groups have formed a glycosidic linkage with glucose moieties). The enzymes responsible for these modifications are encoded by the virus. Figure 22.23 shows the pathway to formation of glucosylated DNA from T-even phage salvage enzymes.