The T4 bacteriophage of E.coli protects its DNA via two glycosyltransferases which glucosylate 5-hydroxymethyl cytosines (5-HMC) using UDP-glucose. These two proteins are the retaining alpha-glucosyltransferase (AGT) and the inverting beta-glucosyltransferase (BGT) [].This entry represents AGT and similar proteins from Uroviricota. AGT catalyses the transfer of glucose from uridine diphosphoglucose to 5-hydroxymethyl cytosine of T4 DNA to yield glucosyl 5-hydroxymethyl cytosine []. This protein adopts the GT-B fold and binds both the sugar donor and acceptor to the C-terminal domain. There is evidence for a role of AGT in the base-flipping mechanism and for its specific recognition of the acceptor base []. AGT interacts with the clamp protein gp45 []. The modification performed by this enzyme protects the phage genome against its own nucleases, the host restriction endonuclease system and against the host CRISPR-Cas9 defence system [].
