Arginine methyltransferase that can both catalyze the formation of omega-N monomethylarginine (MMA) and symmetrical dimethylarginine (sDMA). Specifically mediates the symmetrical dimethylation of SF3B2. Involved in the regulation of alternative splicing of pre-mRNA. L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)'-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Found in a complex with PRMT9, SF3B2 and SF3B4. Interacts with SF3B2. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family. This protein should not be confused with Fbxo11 (AC Q7TPD1) that was initially erroneously named Prmt9.