The three related TET genes, TET1, TET2 and TET3 code respectively for three related mammalian proteins TET1, TET2, and TET3.  All three proteins possess 5mC oxidase activity, but they differ in terms of domain architecture.  TET proteins are large (~180- to 230-kDa) multidomain enzymes.  All TET proteins contain a conserved double-stranded β-helix (DSBH) domain, a cysteine-rich domain, and binding sites for the cofactors Fe(II) and 2-oxoglutarate (2-OG) that together form the core catalytic region in the C terminus.  In addition to their catalytic domain, full-length TET1 and TET3 proteins have an N-terminal CXXC zinc finger domain that can bind DNA.  The TET2 protein lacks a CXXC domain, but the IDAX gene, that's a neighbor of the TET2 gene, encodes a CXXC4 protein.  IDAX is thought to play a role in regulating TET2 activity by facilitating its recruitment to unmethylated CpGs.