Interferon-inducible antiviral protein which plays a major role in the cell antiviral state induced by type I and type II interferon (PubMed:31812350). Catalyzes the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP) via a SAM-dependent radical mechanism (PubMed:29925952, PubMed:30872404). In turn, ddhCTP acts as a chain terminator for the RNA-dependent RNA polymerases from multiple viruses and directly inhibits viral replication (PubMed:29925952). Therefore, inhibits a wide range of DNA and RNA viruses, including human cytomegalovirus (HCMV), hepatitis C virus (HCV), west Nile virus (WNV), dengue virus, sindbis virus, influenza A virus, sendai virus, vesicular stomatitis virus (VSV), zika virus, and human immunodeficiency virus (HIV-1) (PubMed:29925952, PubMed:30587778, PubMed:31921110, PubMed:30934824). Promotes also TLR7 and TLR9-dependent production of IFN-beta production in plasmacytoid dendritic cells (pDCs) by facilitating 'Lys-63'-linked ubiquitination of IRAK1 by TRAF6 (PubMed:30872404). Plays a role in CD4+ T-cells activation and differentiation. Facilitates T-cell receptor (TCR)-mediated GATA3 activation and optimal T-helper 2 (Th2) cytokine production by modulating NFKB1 and JUNB activities. Can inhibit secretion of soluble proteins. AH2 + CTP + S-adenosyl-L-methionine = 3'-deoxy-3',4'-didehydro-CTP + 5'-deoxyadenosine + A + H(+) + H2O + L-methionine Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. IRAK1 and TRAF6 synergistically activate RSAD2 increasing its activity with CTP as substrate about 10-fold. Homodimer. Interacts with IRAK1 and TRAF6 (PubMed:30872404, PubMed:31921110). Interacts with FPPS (PubMed:18005724). Interacts with HADHB (PubMed:21527675). Interacts (via C-terminus) with VAPA/VAP33 (via C-terminus) (PubMed:21957124). (Microbial infection) Interacts with human cytomegalovirus/HHV-5 protein vMIA/UL37; this interaction results in RSAD2/viperin relocalization from the endoplasmic reticulum to the mitochondria. (Microbial infection) Interacts (via N-terminus) with enterovirus A71 protein 2C; this interaction inhibits viral replication. (Microbial infection) Interacts with herpes simplex virus 1/HHV-1 glycoprotein D; this interaction inhibits HHV-1 replication by facilitating IRF7-mediated IFN-beta production. Infection with human cytomegalovirus (HCMV) causes relocation to the Golgi apparatus and to cytoplasmic vacuoles which also contain HCMV proteins glycoprotein B and pp28. Interaction with human cytomegalovirus/HHV-5 protein vMIA/UL37 results in its relocalization from the endoplasmic reticulum to the mitochondria. By interferon type I, type II and bacterial lipopolysaccharides (LPS). Little or no induction by IFNG/IFN-gamma is observed in monocytic cell lines. Induced by infection with hepatitis C virus, yellow fever virus and Sendai virus, presumably through type I interferon pathway. Induction by infection with human cytomegalovirus (HCMV), stomatitis virus (VSV), chikungunya virus (CHIKV), Japanese encephalitis virus (JEV) occurs independent of the IFN pathway. The N-terminal region (1-42) is necessary for its localization to the endoplasmic reticulum membrane and lipid droplet. Acetylated by HAT1. HAT1-mediated acetylation of Lys-197 in turn recruits UBE4A that stimulates RSAD2 polyubiquitination leading to proteasomal degradation. 'Lys-6'-linked polyubiquitination at Lys-206 leads to RSAD2 protein degradation. Up-regulated in atherosclerosis. Latent viruses like HCMV may be involved in atherogenesis by initiating local inflammation. This may induce up-regulation of antiviral gene RSAD2, which modulates lipids synthesis, and thus could play a role in abnormal lipid accumulation leading to atherosclerosis. Belongs to the radical SAM superfamily. RSAD2 family.