Arginine methyltransferase that methylates (mono and asymmetric dimethylation) the guanidino nitrogens of arginyl residues present in target proteins. Constitutes the main enzyme that mediates monomethylation and asymmetric dimethylation of histone H4 'Arg-4' (H4R3me1 and H4R3me2a, respectively), a specific tag for epigenetic transcriptional activation. Methylates ilf3 to regulate its DNA-binding activity. Required for neural induction, playing a key role in the control of epidermal versus neural cell fate choice (By similarity). Methylates cirbp to regulate its subcellular location. Acts transiently during metamorphosis as a transcription coactivator, enhancing thyroid hormone (T3) receptor (TR)-mediated transcription by enhancing TR binding to the T3 response element (TRE), and histone modification through recruitment of other coactivators. L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Homodimer. Homooctamer; individual homodimers associates to form a homooctamer and homooligomerization is required for proper localization to the cell membrane. Individual homodimers can associate to form a homohexamer (By similarity). Component of a complex with lsm14a/rap55a. Interacts with cirbp (By similarity). Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family. Truncated N-terminus.