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 (via MYND-type zinc finger) with EPB41L3. Interacts (via SET domain) with p53/TP53. Interacts with RB1 and HSP90AA1 (By similarity). Interacts with RNA polymerase II and HELZ. Interacts with SIN3A and HDAC1. Highly expressed in heart, skeletal muscle and brain tissue. During cardiac development, it is differentially expressed with highest expression in the neonatal heart while very low expression is detected at 12.5 dpc and adult. Specifically expressed in cardiomyocytes (at protein level). Although specifically expressed in cardiomyocytes, a conditional deletion in heart does not lead to any visible phenotype. Belongs to the class V-like SAM-binding methyltransferase superfamily. The protein was previously thought to dimethylate histone 3 'Lys-36', but this is now known not to take place in vivo. Deletion within an exon that does not correspond to an intron.