Arboviruses are maintained in a natural cycle that requires blood-sucking arthropod and vertebrate hosts. Arboviruses are believed to persistently infect their arthropod host without overt pathology and cause acute infection with viremia in their vertebrate host. We have focused on elucidating how a specific arbovirus, Rift Valley fever (RVF) virus, causes cytopathic effect in cells derived from vertebrates and non-cytopathic infection in cells derived from arthropods. We demonstrate that the vertebrate virulence factor, NSs, is functional in arthropod cells but is expressed at significantly lower levels in infected arthropod versus infected vertebrate cells.

The enzyme N5‐carboxylaminoinidazole ribonucleotide (N5‐CAIR) mutase is found in microbial de novo purine biosynthesis but is absent in humans making it an attractive antimicrobial target. N5‐CAIR mutase catalyzes the synthesis of carboxyaminoimidazole ribonucleotide (CAIR) from N5‐CAIR which is itself prepared from aminoimidazole ribonucleotide (AIR) by the enzyme N5‐CAIR synthetase. During our research on identifying inhibitors of N5‐CAIR mutase, we developed an innovative, fluorescence‐based assay to measure the activity of this enzyme. This assay relies upon our recent serendipitous observation that AIR reversibly reacts with the compound isatin. Reaction of a fluorescently‐tagged isatin with AIR resulted in a large increase in fluorescence intensity allowing a measurement of the concentration of AIR in solution. From this observation, we developed a reproducible, non‐continuous assay that can replicate the known kinetic parameters of the enzyme and can readily detect a recognized inhibitor of the enzyme. This assay should find utility in screening for inhibitors targeting N5‐CAIR mutase.