Double-stranded RNA (dsRNA) is a type of RNA with a complementary strand, similar to cellular DNA. Double-stranded RNAs such as viral RNA or siRNA are able to promote RNA interference in eukaryotic cells and elicit an interferon response in vertebrates. This standard is synthesized in vitro by annealing after transcription with T7 RNA polymerase and four NTPs (ATP, GTP, CTP, UTP) as substrates.