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.