label: histone H4K20 methyltransferase activity
label_lc: histone h4k20 methyltransferase activity
description: "Catalysis of the reaction: S-adenosyl-L-methionine + histone H4 L-lysine (position 20) = S-adenosyl-L-homocysteine + histone H4 N6-methyl-L-lysine (position 20). This reaction is the addition of a methyl group to the lysine residue at position 20 of the histone H4 protein."