The enzyme catalyses the methylation of one of the terminal guanidino nitrogen atoms in arginine residues within proteins, forming monomethylarginine, followed by the methylation of the second terminal nitrogen atom to form a symmetrical dimethylarginine. The mammalian enzyme is active in both the nucleus and the cytoplasm, and plays a role in the assembly of snRNP core particles by methylating certain small nuclear ribonucleoproteins. cf. EC 2.1.1.319, type I protein arginine methyltransferase, EC 2.1.1.321, type III protein arginine methyltransferase, and EC 2.1.1.322, type IV protein arginine methyltransferase.
