Virology 235, 1-9 (1997) Article no. VY978681

New Insights into the Mechanisms of RNA Recombination

Peter D. Nagy and Anne E. Simon

Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003

RNA plays many different roles in biological systems. One of RNAs most intriguing features is the ability to carry genetic information despite a labile nature. While RNA genomes were presumably widespread in the primordial "RNA world," only RNA viruses and viroids continue to exploit RNA-based genetic materials. As with DNA-based organisms, these entities must evolve and adapt in order to survive. Genetic recombination, the formation of chimeric molecules from segments previously separated on the same molecule or present on different parental molecules, is one of the most important mechanisms for generating novel genomes that may have selective advantages over parental genomes. Recent studies on the evolution of RNA viruses have revealed that RNA recombination is a widespread phenomenon that has shaped modern viruses by rearranging viral genomes or disseminating functional modules among different viruses (Strauss and Strauss, 1988; Dolja and Carrington, 1992; Lai, 1992; Simon and Bujarski, 1994). In addition, an important short-term function of genetic recombination may be the rescue of functional sequences from mutated parental molecules, which is of particular significance given the high mutation rates associated with replication by RNA-dependent RNA polymerases (RdRp) (Domingo et a/., 1996). Depending on the precision of the repair mechanism, the repaired genome can be similar to the parental genome, or it can contain further mutations. This illustrates that sequence diversity in RNA sequences generated by genetic recombination can involve both gross changes and minor mutations. More over, the products of recombination can overlap with unrelated phenomena, including mutagenesis and nonrecombination-based genome repair.