Interferon-induced, dsRNA-activated antiviral enzyme which plays a critical role in cellular innate antiviral response (PubMed:10464285, PubMed:9880569). Activated by detection of double stranded RNA (dsRNA): polymerizes higher oligomers of 2'-5'-oligoadenylates (2-5A) from ATP which then bind to the inactive monomeric form of ribonuclease L (RNASEL) leading to its dimerization and subsequent activation (PubMed:10464285, PubMed:9880569, PubMed:11682059). Activation of RNASEL leads to degradation of cellular as well as viral RNA, resulting in the inhibition of protein synthesis, thus terminating viral replication (PubMed:10464285, PubMed:9880569). Can mediate the antiviral effect via the classical RNASEL-dependent pathway or an alternative antiviral pathway independent of RNASEL (PubMed:21142819). In addition, it may also play a role in other cellular processes such as apoptosis, cell growth, differentiation and gene regulation (PubMed:21142819). May act as a negative regulator of lactation, stopping lactation in virally infected mammary gland lobules, thereby preventing transmission of viruses to neonates (By similarity). Non-infected lobules would not be affected, allowing efficient pup feeding during infection (By similarity). 3 ATP = 5'-triphosphoadenylyl-(2'->5')-adenylyl-(2'->5')-adenosine + 2 diphosphate Produced as a latent enzyme which is activated by double stranded RNA (dsRNA) generated during the course of viral infection(PubMed:9880569). The dsRNA activator must be at least 15 nucleotides long, and no modification of the 2'-hydroxyl group is tolerated (PubMed:9880569). ssRNA or dsDNA do not act as activators (PubMed:9880569). Strongly inhibited by copper, iron and zinc ions (PubMed:11682059). Partially inhibited by cobalt and nickel ions (PubMed:11682059). Homodimer. By type I interferon (IFN) and viruses. Myristoylation is not essential for its activity. Glycosylated. Glycosylation is essential for its activity. Belongs to the 2-5A synthase family.