Methylation of arginine residues is a widespread post-translational modification of proteins catalyzed by a small family of PRMTs. The modification appears to regulate protein functions and interactions that affect gene regulation, signalling and subcellular localization of proteins and nucleic acids. Protein arginine methyltransferase 5 (PRMT5) is a member of the protein arginine N-methyltransferases (PRMT)family, and exists as at least homodimers and homotetramers, or homooligomers mediated by disulfide bonds and non-covalent association ubiquitously. PRMT5 specifically mediates the symmetrical dimethylation of arginine residues in the small nuclear ribonucleoproteins Sm D1 (SNRPD1) and Sm D3 (SNRPD3), and thus plays a role in the assembly and biogenesis of snRNP core particles. PRMT5 methylates histone H2A and H4 'Arg-3' during germ cell development, as well as histone H3 'Arg-8', which may repress transcription. PRMT5 also methylates SUPT5H and regulates its transcriptional elongation properties. Additionally, it is also suggested that PRMT5 negatively regulates cyclin E1 promoter activity and cellular proliferation.