Protein-lysine N-methyltransferase involved in the regulation of cell quiescence by catalyzing the trimethylation of 'Lys-20' of histone H4 and 'Lys-79' of histone H3 (H4K20me3 and H3K79me3, respectively) during diapause formation, a state of obligate dormancy. L-lysyl(79)-[histone H3] + 3 S-adenosyl-L-methionine = 3 H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(79)-[histone H3] + 3 S-adenosyl-L-homocysteine L-lysyl(20)-[histone H4] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl(20)-[histone H4] + S-adenosyl-L-homocysteine N(6)-methyl-L-lysyl(20)-[histone H4] + S-adenosyl-L-methionine = H(+) + N(6),N(6)-dimethyl-L-lysyl(20)-[histone H4] + S-adenosyl-L-homocysteine N(6),N(6)-dimethyl-L-lysyl(20)-[histone H4] + S-adenosyl-L-methionine = H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(20)-[histone H4] + S-adenosyl-L-homocysteine Highly expressed in diapause embryos, in which cells were in a quiescent state (at protein level). Belongs to the class V-like SAM-binding methyltransferase superfamily. SETD4 family.