Arginine methyltransferase that methylates (mono and asymmetric dimethylation) the guanidino nitrogens of arginyl residues present in proteins such as ESR1, histone H2, H3 and H4, ILF3, HNRNPA1, HNRNPD, NFATC2IP, SUPT5H, TAF15, EWS, HABP4, SERBP1, RBM15, FOXO1, CHTOP and MAP3K5/ASK1 (PubMed:15327772, PubMed:19858291). 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 (By similarity). May be involved in the regulation of TAF15 transcriptional activity, act as an activator of estrogen receptor (ER)-mediated transactivation, play a key role in neurite outgrowth and act as a negative regulator of megakaryocytic differentiation, by modulating p38 MAPK pathway (By similarity). Methylates RBM15, promoting ubiquitination and degradation of RBM15 (By similarity). Methylates FOXO1 and retains it in the nucleus increasing its transcriptional activity. Methylates CHTOP and this methylation is critical for its 5-hydroxymethylcytosine (5hmC)-binding activity (PubMed:19858291). Methylates MAP3K5/ASK1 at 'Arg-85' and 'Arg-87' which promotes association of MAP3K5 with thioredoxin and negatively regulates MAP3K5 association with TRAF2, inhibiting MAP3K5 stimulation and MAP3K5-induced activation of JNK (By similarity). Methylates H4R3 in genes involved in glioblastomagenesis in a CHTOP- and/or TET1-dependent manner (By similarity). Plays a role in regulating alternative splicing in the heart (PubMed:30321814). L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Homodimer and heterodimer with PRMT8. Homooctamer; individual homodimers associates to form a homooctamer. Individual homodimers can associate to form a homohexamer. Interacts with BTG1, BTG2 and IFNAR1. Interacts with ILF3 and SUPT5H. Interacts with and methylates FOXO1, leading to the nuclear retention of FOXO1 and the stimulation of FOXO1 transcriptional activity. Methylation of FOXO1 is increased upon oxidative stress (By similarity). Interacts with NFATC2IP. Interacts with and methylates CHTOP, thereby enabling the interaction of CHTOP with the 5FMC complex. Interacts with and probably methylates ATXN2L (By similarity). Component of the methylosome, a 20S complex containing at least CLNS1A/pICln, PRMT5/SKB1, WDR77/MEP50, PRMT1 and ERH (By similarity). Interacts with DHX9 (via RGG region) (By similarity). Interacts (via N-terminus) with HABP4 (By similarity). Interacts with MAP3K5/ASK1; the interaction results in MAP3K5 methylation by PRMT1 which inhibits MAP3K5 activation (By similarity). Interacts with TRIM48; the interaction results in ubiquitination of PRMT1 by TRIM48, leading to PRMT1 proteasomal degradation and activation of MAP3K5 (By similarity). Mostly found in the cytoplasm (PubMed:19858291). Colocalizes with CHTOP within the nucleus (PubMed:19858291). Low levels detected also in the chromatin fraction (PubMed:22872859). Expressed in the heart where it is detected in both cardiomyocytes and non-myocytes (at protein level). Polyubiquitinated at Lys-145 by the SCF(FBXL17) complex, leading to its subsequent degradation (PubMed:28883095). Ubiquitination is regulated by acetylation at Lys-228 and Lys-233 (PubMed:28883095). Polyubiquitinated by E3 ubiquitin-protein ligase TRIM48, leading to suppression of MAP3K5/ASK1 methylation and subsequent MAP3K5 activation (By similarity). Acetylation at Lys-228 and Lys-233 regulates ubiquitination by the SCF(FBXL17) complex. Acetylated at Lys-233 by p300/EP300. Deacetylated at Lys-228 and Lys-233 by SIRT1. Conditional knockout in cardiomyocytes results in dilated cardiomyopathy in juveniles and death within 60 days of birth with aberrant splicing occurring in a number of genes including Ktn1, Lmo7, Mef2a, Tmed2, Snap23, Sorbs1 and Ttn. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family.