Histone methyltransferase that specifically monomethylates 'Lys-4' of histone H3. H3 'Lys-4' methylation represents a specific tag for epigenetic transcriptional activation. Plays a central role in the transcriptional activation of genes such as collagenase or insulin. Recruited by IPF1/PDX-1 to the insulin promoter, leading to activate transcription. Has also methyltransferase activity toward non-histone proteins such as p53/TP53, TAF10, and possibly TAF7 by recognizing and binding the [KR]-[STA]-K in substrate proteins. Monomethylates 'Lys-189' of TAF10, leading to increase the affinity of TAF10 for RNA polymerase II. Monomethylates 'Lys-372' of p53/TP53, stabilizing p53/TP53 and increasing p53/TP53-mediated transcriptional activation. L-lysyl(4)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl(4)-[histone H3] + S-adenosyl-L-homocysteine Interacts with IPF1/PDX-1. Expressed during all pre-implementation stages in both male and female embryos. The SET domain is necessary but not sufficient for histone methyltransferase activity. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. SET7 subfamily.