Protein-lysine N-methyltransferase that methylates both histones and non-histone proteins, including p53/TP53 and RB1. Specifically trimethylates histone H3 'Lys-4' (H3K4me3) in vivo. The activity requires interaction with HSP90alpha. Shows even higher methyltransferase activity on p53/TP53. Monomethylates 'Lys-370' of p53/TP53, leading to decreased DNA-binding activity and subsequent transcriptional regulation activity of p53/TP53. Monomethylates RB1 at 'Lys-860'. L-lysyl(4)-[histone H3] + 3 S-adenosyl-L-methionine = 3 H(+) + N(6),N(6),N(6)-trimethyl-L-lysyl(4)-[histone H3] + 3 S-adenosyl-L-homocysteine L-lysyl-[protein] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl-[protein] + S-adenosyl-L-homocysteine Interacts with RNA polymerase II and HELZ. Interacts with SIN3A and HDAC1. Interacts (via MYND-type zinc finger) with EPB41L3. Interacts (via SET domain) with p53/TP53. Interacts with RB1 and HSP90AA1 (By similarity). During fetal muscle development, expression increases from 33 to 90 dpc. Belongs to the class V-like SAM-binding methyltransferase superfamily.