label: histone H4K20 trimethyltransferase activity
label_lc: histone h4k20 trimethyltransferase activity
description: "Catalysis of the reaction: L-lysyl(20)-[histone H4] + 3 S-adenosyl-L-methionine = 3 H+ + N(6),N(6),N(6)-trimethyl-L-lysyl(20)-[histone H4] + 3 S-adenosyl-L-homocysteine. This reaction is the addition of three methyl groups to the lysine residue at position 20 of the histone H4 protein, producing histone H4K20me3."