replication. In contrast, uninfected mammalian cells generally produce dsRNA helices of fewer than 24 base pairs during transcription. Cell death is effected via one of the last steps in the apoptosis pathway in which complexes containing intracellular apoptosis signalling molecules simultaneously bind multiple procaspases. The procaspases transactivate via cleavage, activate additional caspases in the cascade, and cleave a variety of cellular proteins, thereby killing the cell. It has been shown that DRACOs are nontoxic in 11 mammalian cells types and effective against 15 different viruses. References External links Anti–RNA virus drugs Massachusetts Institute of Technology