Characterization of the double-stranded RNA implicated in the inhibition of protein synthesis in cells infected with a mutant adenovirus defective for VA RNA.
In the absence of VA RNAI, protein synthesis in adenovirus-infected HeLa cells fails at late times of infection because of defective initiation. The defect is due to the activation of a protein kinase that phosphorylates the alpha-subunit of initiation factor eIF-2. The kinase responsible for the translational defect is DAI, the double-stranded RNA (dsRNA)-activated inhibitor of protein synthesis, which is present in uninfected HeLa cells at a basal level and in a largely inactive, latent state. In vitro it can be activated by incubation with ATP and low concentration of dsRNA. Previous studies suggested that RNA generated during the course of infection can activate DAI. We show here that the activator RNA has the properties of dsRNA: it chromatographs with dsRNA, can be denatured and reannealed, and is destroyed by a dsRNA-specific nuclease. At least some of the dsRNA is viral. It hybridizes to DNA sequences in the center of the viral genome, principally between map units 47 and 51 and 73 and 76, consistent with an origin in the symmetrical transcription of both viral DNA strands.