Evidence for secondary structure within the virion RNA of echovirus 22

Phenol-extracted echovirus 22 virion RNA is infectious, but unlike poliovirus virion RNA, it resists digestion with pancreatic RNase and nuclease P-1, a 3' exonuclease selective for single-stranded RNA. These data indicate the presence of an enzyme-resistant portion somewhere in the RNA molecule and suggest that it is a double-stranded or base-paired region distant from the unblocked 3' terminus. Equilibrium density gradient centrifugation of native echovirus 22 virion RNA results in a single peak with a density of 1.63 g/cm3. When sheared before centrifugation, the molecule is resolved into two RNA species: one with an approximate density of 1.70 to 1.71 g/cm3, as is observed also for single-stranded poliovirus virion RNA, and the other with a density of 1.58 to 1.59 g/cm3. Data obtained from rate zonal centrifugation may be used to calculate an approximate sedimentation coefficient corrected to water at 20 degrees C of 34 and a molecular weight of 2.4 X 10(6) for the virion RNA. We propose a model for echovirus 22 RNA composed of a linear RNA molecule with a 5' hairpin.