Interferon-inducible antiviral protein which plays a major role in the cell antiviral state induced by type I and type II interferon. Catalyzes the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP) via a SAM-dependent radical mechanism. In turn, ddhCTP acts as a chain terminator for the RNA-dependent RNA polymerases from multiple viruses and directly inhibits viral replication. Therefore, inhibits a wide range of DNA and RNA viruses (By similarity). 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. 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 (By similarity) (PubMed:17686841, PubMed:19047684, PubMed:21435586, PubMed:21880757). 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:21435586). Interacts with FPPS. Interacts with HADHB. Interacts (via C-terminus) with VAPA/VAP33 (via C-terminus) (By similarity). Expressed at higher levels in atherosclerotic arteries than in normal arteries. By interferon type I, type II and LPS. Induced by infection with Vesicular stomatitis virus and pseudorabies virus in dendritic cells, presumably through type I interferon pathway. The N-terminal region (1-43) is necessary for its localization to the endoplasmic reticulum membrane and lipid droplet. Acetylated by HAT1. HAT1-mediated acetylation of Lys-198 in turn recruits UBE4A that stimulates RSAD2 polyubiquitination leading to proteasomal degradation. 'Lys-6'-linked polyubiquitination at Lys-207 leads to RSAD2 protein degradation. Belongs to the radical SAM superfamily. RSAD2 family. Truncated C-terminus.