INTRODUCTION
Segmented genome RNA viruses that infect animals include the Reoviridae, Orthomyxoviridae, Arenaviridae, and Bunyaviridae virus families. The Reoviridae have genome RNA segments that code for single polypeptide species. Seven of the eight RNA species of the orthomyxovirus induenza also code for single polypeptide species, while the eighth codes for two nonstructural polypeptides, NSI and NS2. Although all the coding assignments of the arenaviruses and bunyaviruses have yet to be determined, from the number of their viral RNA segments and the identified virion polypeptides, it is probable that for each family of viruses, one or more of the viral RNA segments codes for more than one polypeptide. For example, members of the Arenaviridae have two viraL RNA segments and three or four virion polypeptides, while bunyaviruses, have three viral RNA segments and four virion polypeptides.
The studies discussed in this paper concern our ongoing analyses of the stucture, genetic potential, and coding assignments of bunyaviruses and arenaviruses. To investigate some of these questions, using selected members of each family, we have obtained recombinant viruses derived from heterologous temperature-sensitive or wild-type virus coinfections, analyzed their genotypes and virion polypeptides, and thereby determined the origin of their gene products. In addition, we have initiated studies to relate this information to the pathogenic potential of the recombinant viruses in order to determine if a single viral gene product is the major determinant of pathogenicity for these viruses.