Arginine methylation is a prevalent post-translational modification found on both nuclear and cytoplasmic proteins. The methylation of arginine residues is catalyzed by the protein arginine N-methyltransferase (PRMT) family of enzymes. Proteins that are arginine methylated are involved in a number of different cellular processes, including transcriptional regulation, RNA metabolism and DNA damage repair (Bedford and Richard, 2005). Most PRMTs methylate glycine-and arginine-rich patches (GAR motifs) within their substrates. The complexity of the methylarginine mark is enhanced by the ability of this residue to be methylated in three different ways on the guanidino group: monomethylated (MMA), symmetrically dimethylated (sDMA) and asymmetrically dimethylated (aDMA), each of which has potentially different functional consequences.