Activity of Toscana and Rift Valley fever virus transcription complexes onheterologous templates

A transcription system for Toscana virus (TOSV) (a member of the family Bun yaviridae, genus Phlebovirus) was constructed. For in vivo expression, the TOSV transcription system uses the viral N and L proteins and an S-like RNA genome containing the chloramphenicol acetyltransferase reporter gene in t he antisense orientation Ranked by the viral genomic 5'- and 3'-terminal S sequences. It was found that the N and L proteins represent the minimal pro tein requirement for an active transcription complex. To investigate the po ssibility of reassortment between TOSV and Rift Valley fever virus (RVFV), the activity of their polymerase complexes was tested on their heterologous S-like RNA genomes and this showed that both virus complexes were active. Moreover, hybrid transcriptase complexes with protein components originatin g from the two viruses were tested on both virus templates and only the com bination RVFV L + TOSV N on RVFV S-like RNA was found to be active in this assay. These results suggest that virus reassortants might be generated whe never the two viruses infect the same host.