The function of SMYD3 (SET and MYND domain containing 3, Ensembl gene identifier ENSG00000185420) is as follows. Histone methyltransferase. Specifically methylates 'Lys-4' of histone H3, inducing di- and tri-methylation, but not monomethylation (PubMed:15235609, PubMed:22419068). Also methylates 'Lys-5' of histone H4 (PubMed:22419068). Plays an important role in transcriptional activation as a member of an RNA polymerase complex (PubMed:15235609). Binds DNA containing 5'-CCCTCC-3' or 5'-GAGGGG-3' sequences (PubMed:15235609). {ECO:0000269|PubMed:15235609, ECO:0000269|PubMed:22419068}.