Double-stranded RNA from Sindbis virus-infected chick, hamster, and mosquito cells was characterized in sucrose gradients. The ds RNA was identified by its resistance to RNase and by immunochemical methods using antibodies specifically reactive with multistrand polyribonucleotides. Each of the three cell types contained 20 S ds RNA. The BHK21 and chick cells contained large amounts of ds RNA with lower sedimentation constants (12 S in the former, and 15 S and 12 S in the latter case). In the mosquito cells, in contrast, only a small amount of ds RNA smaller than 20 S was found. In each case the relative amount of the smaller species increased with time after infection. An immunochemical binding assay to detect radioactively labeled ds RNA was adapted for use in these experiments.
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