Introduction

The majority of the significant human pathogenic viruses have RNA genomes. Hepatitis C, influenza, measles, yellow fever, dengue, Lassa, and Ebola hemorrhagic fevers are but a few examples of diseases caused by RNA viruses that are responsible for considerable morbidity and mortality. However, studies on the molecular biology of viruses with RNA genomes were hampered for many years by the inherent limitations imposed by the nature of the genetic material. In contrast, the development of analogous techniques for negative-strand RNA viruses was slower, partly because neither genome nor antigenome RNA is infectious unlike positive-strand viruses. The negative-sense viral RNA is assembled with the viral nucleocapsid protein into a ribonucleoprotein (RNP) complex, and it is the RNP that is the template for all RNA synthetic events and the initiation of infection. Reconstitution of RNP complexes from isolated components proved to be technically demanding.