Characterization of a temperature-sensitive defect of enterovirus 70: effect of elevated temperature on in vitro transcription.

A crude replication complex prepared from enterovirus 70-infected cells was used to study the temperature-sensitive characteristic of the virus. The complex showed a temperature sensitivity in the in vitro incorporation of radiolabeled ribonucleoside triphosphate. The endonuclease itself did not account for the restricted RNA synthesis at the nonpermissive temperature. Analyses of the in vitro products by both gel electrophoresis and sucrose density gradient centrifugation showed that the complex synthesized three types of viral RNA only when incubated for a short period of time at the nonpermissive temperature. When the replication complex was treated with a detergent (deoxycholic acid), incorporation of ribonucleoside triphosphate into RNA at the permissive temperature was reduced to the level of that at the nonpermissive temperature. In addition, the in vitro RNA synthesis by the enterovirus 70 replication complex at the permissive temperature required a higher concentration of ATP than of other ribonucleoside triphosphates, whereas such a preference for ATP was not found in the reaction at the nonpermissive temperature. The results indicate that the initiation step of RNA synthesis by the complex is blocked at the nonpermissive temperature. The possible implications of these findings are discussed.