On the Specificity of Bacteriophage‐Induced Hydroxymethylcytosine Glucosyltransferases

Glucose-less DNA of the T-even bacteriophage type was glucosylated in vitro by the T4-specific hydroxymethylcytosine α- and β-glucosyltransferases separately and by mixtures of the two enzymes in the presence of varying concentrations of Mg++ ions. The α- and β-glucose content of the glucosylated 5-hydroxymethylcytosine residues in the recovered DNA was analyzed. The results indicate that the 5-hydroxymethylcytosine-α-glucosyltransferase is not capable of glucosylating hydroxymethyldeoxyctidine nucleotide, whereas the β-glucosyltransferase will react with such 5-hydroxymethyldeoxycytidine nucleotide, whereas the β-glucosyltransferase will react with such 5-hydroxymethylcytosine residues. 5-Hydroxymethyldeoxycytidine nucleotides in all the other sequences examined are susceptible to both enzymes. In the presence of both transferases the ratio of α- and β-glucose residues introduced in vitro can be influenced by changing the Mg++ content of the incubation mixture. This situation applies to 5-hydroxymethylcytosine residues generally and to the 5-hydroxymethylcytosine nucleotides present in some specific sequences. The proportion of α- and β-glucosides in T4 DNA produced in vivo has been found to remain constant irrespective of the Mg++ content of the growth medium.