Evolution: Zapping viral RNAs

Abstract

The discovery that the host defence protein ZAP specifically targets viral RNAs that are rich in a particular pair of adjacent bases — cytosine followed by guanine — sheds light on the evolution of viral RNA genomes.

Figure 1. ZAP protein selectively binds and blocks specific RNA viruses

a, Many RNA viruses have low levels of CG — a cytosine base followed by a guanine. Takata et al. demonstrate that this low CG content prevents the host-derived defence protein ZAP (zinc-finger antiviral protein) from binding viral RNA that enters the cell cytoplasm, and so enables viral replication. b, When the authors engineered an RNA virus to have high levels of CG, they found that ZAP selectively bound to CG-rich sequences through its four finger domains. Once bound, ZAP recruits a protein complex called the RNA exosome to degrade viral RNA, thus preventing viral replication.