Notes: Protein Arginine Methyltransferases (PRMTs) are S-adenosyl-L-methionine-dependent enzymes that catalyze post-translational modification of arginine residues by methylation in three different ways: monomethylation, symmetric dimethylation, or asymmetric dimethylation at terminal arginine guanidino nitrogen atoms.{18900} Class I PRMTs catalyze arginine monomethylation and asymmetric dimethylation. PRMT1 is a class I arginine methyltransferase that methylates arginine residues at a number of glycine and arginine rich regions (GAR motifs) in proteins including histone H4 at arginine 3.{18899}