Arginine methyltransferase that methylates the guanidino nitrogens of arginyl residues in proteins such as histones. Involved in growth regulation (By similarity). Involved in embryonic dorsal development. L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Interacts with ctnnb1. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family. Extended N-terminus.