label: histone H4K20 monomethyltransferase activity
label_lc: histone h4k20 monomethyltransferase activity
description: "Catalysis of the reaction: L-lysyl20-[histone H4] + S-adenosyl-L-methionine = H+ + N6-methyl-L-lysyl20-[histone H4] + S-adenosyl-L-homocysteine. This reaction is the addition of a methyl group to the unmethylated lysine residue at position 20 of histone H4, producing histone H4K20me."