S-adenosyl-L-methionine-dependent and membrane-associated arginine methyltransferase that can both catalyze the formation of omega-N monomethylarginine (MMA) and asymmetrical dimethylarginine (aDMA). L-arginyl-[protein] + S-adenosyl-L-methionine = H(+) + N(omega)-methyl-L-arginyl-[protein] + S-adenosyl-L-homocysteine L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Homodimer. Tetramer; individual homodimers associates to form a homotetramer. Homooctamer; individual homodimers associates to form a homooctamer and homooligomerization is required for proper localization to the cell membrane. The N-terminal region (1-60) inhibits the arginine N-methyltransferase activity. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family. PRMT8 subfamily.