The Bedford Laboratory studies the biological role of arginine methylation, a very common post-translational modification present on histones and other proteins. With regards to histones, arginine methylation plays an important role in the histone code and epigenetic memory. We focus on the family of proteins responsible for methylating arginine residues, protein arginine methyltransferase (PRMTs). Arginine is unique among amino acids as its guanidino group contains five potential hydrogen bond donors that are positioned for favorable interactions with biological hydrogen bond acceptors. Three types of methylarginine species exist: monomethylarginine (MMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). The formation of MMA, ADMA, and SDMA in mammalian cells is performed by a family of nine protein arginine methyltransferases (PRMTs).