Learning noncoding RNA biology from viruses.

Insights into interactions between viral factors and the cellular machinery usually lead to discoveries concerning host cell biology. Thus, the gene expression field has historically relied on viral model systems to discover mechanisms underlying different cellular processes. In recent years, the functional characterization of the small nuclear noncoding RNAs expressed by the oncogenic Herpesvirus saimiri, called HSURs, resulted in the discovery of two mechanisms for the regulation of gene expression. HSUR1 and HSUR2 associate with host microRNAs, which are small noncoding RNAs that broadly regulate gene expression by binding to messenger RNAs. HSUR1 provided the first example of a process known as target-directed miRNA degradation that operates in cells to regulate miRNA populations. HSUR2 functions as a miRNA adaptor, uncovering an entirely new, indirect mechanism by which miRNAs can inhibit mRNA function. Here, I review the path that led to these discoveries and their implications and postulate new exciting questions about the functions of these fascinating viral noncoding RNAs.