Virus Interference by Cellular Double-Stranded Ribonucleic Acid

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Ribonuclease-resistant ribonucleic acid (RNA) was isolated from uridine-labeled cultures of rabbit kidney, chicken embryo, and HeLa cells. This RNA, regardless of its source, was found to induce interference with virus growth in either rabbit kidney or chicken embryo cultures. Nuclease-treated cellular nucleic acids exhibited interference-inducing activity which eluted with a small fraction of RNA in the exclusion volume of a 6% agarose gel column. Besides resistance to ribonucleases, the interference inducer and RNA isolated from partially digested nucleic acids have in common two properties of double-stranded RNA: (i) similar sharp melting profiles were obtained for inducer and ribonuclease-resistant RNA, with Tm dependent on NaCl concentration; (ii) ribonuclease-resistant inducer and RNA banded together in Cs2SO4 density gradients at a density characteristic of known double-stranded RNA. After melting at low ionic strength, the labeled RNA shifted to a higher density and its capacity to inhibit virus replication was lost. Velocity sedimentation analysis of the cellular ribonuclease-resistant RNA indicated that the majority sedimented between 7 and 11S, but only RNA sedimenting at ≧8 to 20S had a high specific activity of interference induction. Without prior ribonuclease treatment, the ribonuclease-resistant RNA can be precipitated with 2 m LiCl and thus appears to exist in purified cellular nucleic acids as part of molecular complexes with both single- and double-stranded regions of RNA. The biosynthesis of cellular double-stranded RNA is inhibited by actinomycin D.

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