Base J is a DNA modification found in the genome of Trypanosoma brucei and all 
other kinetoplastids analyzed, where it replaces a small fraction of Ts, mainly 
in telomeric and chromosome-internal transcription initiation and termination 
regions. The synthesis of base J is a two-step process whereby a specific T is 
converted to HOMedU (hydroxymethyldeoxyuridine) and subsequently glucosylated to 
generate J. The thymidine hydroxylases (JPB1 and JBP2) that catalyze the first 
step have been characterized, but the identity of the glucosyltransferase 
catalyzing the second step has proven elusive. Recent bioinformatic analysis by 
Iyer et al. (Nucleic Acids Res 2013;41:7635) suggested that Tb927.10.6900 
encodes the glucosyltransferase (HmdUGT) responsible for converting HOMedU to J 
in T. brucei. We now present experimental evidence to validate this hypothesis; 
null mutants of Tb927.10.6900 are unable to synthesize base J. Orthologues from 
related kinetoplastids show only modest conservation, with several insertion 
sequences found in those from Leishmania and related genera.