Genetic manipulation of non-segmented negative-strand RNA viruses.

Negative-strand RNA viruses are a large and diverse group of enveloped viruses of both medical and economic significance. They are found in hosts from the plant and animal kingdoms, and have a wide range of morphologies, biological properties and genome organizations. A major distinction is made between viruses whose genome consists of a single RNA molecule (order Mononegavirales), including the families Rhabdoviridae, Paramyxoviridae and Filoviridae, and those possessing multipartite (segmented) genomes, comprising the families Orthomyxoviridae (six to nine segments), Bunyaviridae (three segments) and Arenaviridae (two segments) (Pringle, 1991). Particular elements essential for their replication and gene expression have been retained throughout the negative-strand RNA viruses and illustrate that they have originated from a common ancestor (for review see Tordo et al., 1992). Genetic manipulation and analysis of negative-strand RNA virus biology has lagged far behind that of other RNA viruses. In contrast to positive-strand RNA viruses, isolated genome or antigenome RNAs of negative-strand RNA viruses are not infectious. The initiation of an infectious cycle requires the presence of a complete nucleocapsid structure. Only in this form can the RNA function as a template for the virus polymerase. Techniques to introduce recombinant RNA into the genome of a negative-strand RNA virus were first described for the segmented influenza virus (for a recent review see GarciaSastre & Palese, 1993). In this article, the most recent developments in the genetic manipulation of nonsegmented viruses are briefly summarized. Successful rescue of defective rhabdoand paramyxovirus model genomes, and the recovery of infectious rabies virus and recently vesicular stomatitis virus (VSV), measles virus and Sendal virus entirely from cDNA, illustrate that