ADAR1 Restricts Poliovirus Infection through dual disruption of translation initiation and protein coding

Viral RNAs (vRNAs) interact with hundreds of host proteins, but how these interactions shape viral infection remains largely unknown. Here we developed a mass-spectrometry approach to identify cellular RNA-binding proteins (RBPs) that enhance or inhibit infection by modulating vRNA translation. We identified 130 RBPs that associate with polysomes in human cells infected with poliovirus, including known regulators of cap-independent translation from the viral internal ribosome entry site (IRES). We find that adenosine deaminase acting on RNA (ADAR1) is recruited to polysomes during infection and edits 3 sites in the vRNA, reducing viral replication. Two edits occur in the IRES and impair internal translation initiation, while the third edit occurs in the coding region and triggers an amino acid substitution. Incorporation of this threonine-to-alanine mutation into the viral genome attenuated replication. We conclude that ADAR1 restricts poliovirus infection by both reducing vRNA translation and introducing a recurrent coding error.