p72 DEAD box RNA helicase is required for optimal function of the zinc-finger antiviral protein

The zinc-finger antiviral protein (ZAP) specifically inhibits the replication of many viruses by preventing the accumulation of viral mRNAs in the cytoplasm. ZAP directly binds to the viral mRNAs and recruits the RNA exosome to degrade the target RNA. In the present study, we identified the p72 DEAD box RNA helicase, but not the highly similar RNA helicase p68, as a ZAP-interacting protein. The binding domain of ZAP was mapped to its N-terminal portion, whereas both the N- and C-terminal domains of p72 bound to ZAP. Overexpression of the C-terminal domain of p72 reduced ZAP's activity, whereas overexpression of the full-length p72 enhanced ZAP's activity. The RNA helicase activity was required for p72 to promote ZAP-mediated RNA degradation. Depletion of p72 by RNAi also reduced ZAP's activity but did not affect tristetraprolin-mediated RNA degradation. We conclude that p72 is required for the optimal activity of ZAP, and we propose that p72 helps to restructure the ZAP-bound target mRNA for efficient degradation.