JMJD2b belongs to the JMJD2 family of histone demethylases which play an important role in the establishment of the histone code. JMJD2b specifically demethylates the trimethylated K9 of histone H3. It is not able to demethylate K4, K27 and K36 of histone H3, nor K20 of histone H4.