Dioxygenase that catalyzes the first step of DNA base J (beta-d-glucosyl-HOMedU) biosynthesis by converting thymine to 5-hydroxymethyluracil (HOMedU). DNA base J is a hypermodified thymidine residue found in the genome of kinetoplastid parasites, which is localized primarily to repetitive DNA, namely the telomeres, and is implicated in the regulation of antigenic variation. Also specifically binds to base J-containing DNA (J-DNA). Involved in propagation and maintenance of DNA base J synthesis initiated by JBP2 by specifically binding already synthesized DNA base J and propagating J synthesis. Thymine dioxygenase activity and J-DNA-binding are independent functions.

> 85% as determined by SDS-PAGE.