label: histone H3 methyltransferase activity
label_lc: histone h3 methyltransferase activity
description: "Catalysis of the reaction: S-adenosyl-L-methionine + a histone H3 = S-adenosyl-L-homocysteine + a methylated histone H3. Histone methylation generally occurs on either an arginine or a lysine residue."