KDM6B (Lysine demethylase 6B) is a 1,679 amino acid nuclear protein that contains one JmjC domain and belongs to the highly conserved JmjC domain-containing protein family. Functioning as a histone demethylase, JMJD3 uses iron and ascorbate as cofactors to demethylate dimethylated and trimethylated Lys-27 residues of Histone H3, thereby playing an important role in the modification of the histone code.