A double-stranded beta helix (DSBH) fold domain of the 2-oxoglutarate (2OG)-Fe(II)-dependent dioxygenase (2OGFeDO) superfamily found in various eukaryotes, bacteria and bacteriophages [1]. Members of this family catalyze nucleic acid modifications, such as thymidine hydroxylation during base J synthesis in kinetoplastids [2], and the conversion of 5 methyl-cytosine (5-mC) to 5-hydroxymethyl-cytosine (hmC) [3], or further oxidation to 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC) [4]. Metazoan TET proteins contain a cysteine-rich region inserted into the core of the DSBH fold. Vertebrate TET proteins are oncogenes that are mutated in various myeloid cancers [5]. Fungal and algal versions of this family are linked to a predicted transposase and show lineage-specific expansions [1].

1: Prediction of novel families of enzymes involved in oxidative and other complex modifications of bases in nucleic acids. Iyer LM, Tahiliani M, Rao A, Aravind L; Cell Cycle. 2009;8:1698-1710. PMID:19411852

2: Two thymidine hydroxylases differentially regulate the formation of glucosylated DNA at regions flanking polymerase II polycistronic transcription units throughout the genome of Trypanosoma brucei. Cliffe LJ, Siegel TN, Marshall M, Cross GA, Sabatini R; Nucleic Acids Res. 2010;38:3923-3935. PMID:20215442

3: Conversion of 5-methylcytosine to 5-hydroxymethylcytosine in mammalian DNA by MLL partner TET1. Tahiliani M, Koh KP, Shen Y, Pastor WA, Bandukwala H, Brudno Y, Agarwal S, Iyer LM, Liu DR, Aravind L, Rao A; Science. 2009;324:930-935. PMID:19372391

4: Tet-Mediated Formation of 5-Carboxylcytosine and Its Excision by TDG in Mammalian DNA. He YF, Li BZ, Li Z, Liu P, Wang Y, Tang Q, Ding J, Jia Y, Chen Z, Li L, Sun Y, Li X, Dai Q, Song CX, Zhang K, He C, Xu GL; Science. 2011; [Epub ahead of print] PMID:21817016

5: Impaired hydroxylation of 5-methylcytosine in myeloid cancers with mutant TET2. Ko M, Huang Y, Jankowska AM, Pape UJ, Tahiliani M, Bandukwala HS, An J, Lamperti ED, Koh KP, Ganetzky R, Liu XS, Aravind L, Agarwal S, Maciejewski JP, Rao A; Nature. 2010;468:839-843. PMID:21057493