Reassortment Continuum

Abstract

Among the animal viruses only RNA-containing viruses are known to possess segmented genomes. Specifically, five out of approximately a dozen different RNA virus families contain viruses with multiple RNA segments. These viral families comprise the arenaviruses [1], the birnaviruses [2], the bunyaviruses [3], the influenza viruses [4], and the reoviruses [5] (Table 1). Although these viruses share few biological properties, have different host-cell specificities, and replicate in quite different manners, they all have the capacity to reassort their genes during replication. For example, when two different influenza A viruses infect the same cell, the eight RNA segments may be rearranged in such a way as to give rise to 254 possible different reassortants (plus the two parent strains). This exchange of RNA segments (minichromosomes) during viral replication is called reassortment, although it is often (incorrectly) referred to in the literature as recombination, which implies the breakage and linkage of nucleotide bonds. True recombination has been observed with RNA viruses such as picornaviruses [6] and it may also occur among members of the above-mentioned virus families, but the present paper does not deal with this aspect of genetic interaction of segmented RNA viruses. Rather, reassortment will be discussed here as it relates to the replication of viruses in nature, and to possible applications in the laboratory.