Analyses of SELEX-derived ZAP-binding RNA aptamers suggest that the binding specificity is determined by both structure and sequence of the RNA.

The zinc-finger antiviral protein (ZAP) is a host factor that specifically inhibits the replication of certain viruses, including murine leukemia virus, Sindbis virus and Ebola virus, by targeting the viral mRNAs for degradation. ZAP directly binds to the target viral mRNA and recruits the cellular RNA degradation machinery to degrade the RNA. No significant sequence similarity or obvious common motifs have been found in the so far identified target viral mRNAs. The minimum length of the target sequence is about 500 nt long. Short workable ZAP-binding RNAs should facilitate further studies on the ZAP-RNA interaction and characterization of such RNAs may provide some insights into the underlying mechanism. In this study, we used the SELEX method to isolate ZAP-binding RNA aptamers. After 21 rounds of selection, ZAP-binding aptamers were isolated. Sequence analysis revealed that they are G-rich RNAs with predicted stem-loop structures containing conserved "GGGUGG" and "GAGGG" motifs in the loop region. Insertion of the aptamer sequence into a luciferase reporter failed to render the reporter sensitive to ZAP. However, overexpression of the aptamers modestly but significantly reduced ZAP's antiviral activity. Substitution of the conserved motifs of the aptamers significantly impaired their ZAP-binding ability and ZAP-antagonizing activity, suggesting that the RNA sequence is important for specific interaction between ZAP and the target RNA. The aptamers identified in this report should provide useful tools to further investigate the details of the interaction between ZAP and the target RNAs.