5-hydroxymethyluracil (hmU) is an oxidative DNA lesion and a potential intermediate in DNA repair–coupled DNA demethylation pathways. Isotopic labeling and MS reveal that hmU is produced directly by Tet-mediated oxidation of thymine in mouse embryonic stem cells, suggesting a functional role for hmU in stem cells.
- Toni Pfaffeneder
- Fabio Spada
- Thomas Carell