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). The proteins in this family are AGT. AGT 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 [1].

1: Structural evidence of a passive base-flipping mechanism for AGT, an unusual GT-B glycosyltransferase. Lariviere L, Sommer N, Morera S; J Mol Biol. 2005;352:139-150. PMID:16081100