The chemical reactions and pathways involving base J (beta-D-glucosyl-hydroxymethyluracil), a hypermodified thymidine residue found in the genome of kinetoplastid parasites. This modified base is localized primarily to repetitive DNA, namely the telomeres, and is implicated in the regulation of antigenic variation. The base is synthesized in a two-step pathway. Initially, a thymidine residue in DNA is hydroxylated by a thymidine hydroxylase (TH) to form the intermediate hydroxymethyluracil, which is then glucosylated to form base J.