JMJD6 catalyses demethylation of mono- or di-methylated arginine-3 of histone H3 (H3R2Me1/2) and arginine-4 of histone H4 (H4R3Me1/2) (Chang et al. 2007). Non-histone substrates of JMJD6 arginine demethylation have also been reported (Poulard et al. 2014, Lawrence et al. 2014). Subsequent to its characterization as an arginine demethylase, JMJD6 was reported to be a lysine hydroxylase (Webby et al 2009).