New roles for large and small viral RNAs in evading host defences.

It has been known for decades that some clinically important viruses encode abundant amounts of non-coding RNAs (ncRNAs) during infection. Until recently, the number of viral ncRNAs identified was few and their functions were mostly unknown. Although our understanding is still in its infancy, several recent reports have identified new functions for viral microRNAs and larger ncRNAs. These results so far show that different classes of viral ncRNAs act to autoregulate viral gene expression and evade host antiviral defences such as apoptosis and the immune response.