Nuclear localization of influenza B polymerase proteins and their binary complexes

Knowns and unknowns of influenza B viruses

Influenza B viruses (IBVs) circulate annually along with influenza A (IAV) strains during seasonal epidemics. IBV can dominate influenza seasons and cause severe disease, particularly in children and adolescents. Research has revealed interesting aspects of IBV and highlighted the importance of these viruses in clinical settings. Yet, many important questions remain unanswered. In this review, the clinical relevance of IBV is emphasized, unique features in epidemiology, host range and virology are highlighted and gaps in knowledge pinpointed. Multiple aspects of IBV epidemiology, evolution, virology and immunology are discussed. Future research into IBV is needed to understand how we can prevent severe disease in high-risk groups, especially children and elderly.

Inhibition of influenza A virus replication by influenza B virus nucleoprotein: an insight into interference between influenza A and B viruses

Given that co-infection of cells with equivalent titers of influenza A and B viruses (FluA and FluB) has been shown to result in suppression of FluA growth, it is possible that FluB-specific proteins might hinder FluA polymerase activity and replication. We addressed this possibility by individually determining the effect of each gene of FluB on the FluA polymerase assay and found that the nucleoprotein of FluB (NP(FluB)) inhibits polymerase activity of FluA in a dose-dependent manner. Mutational analyses of NP(FluB) suggest that functional NP(FluB) is necessary for this inhibition. Slower growth of FluA was also observed in MDCK cells stably expressing NP(FluB). Further analysis of NP(FluB) indicated that it does not affect nuclear import of NP(FluA). Taken together, these findings suggest a novel role of NP(FluB) in inhibiting replication of FluA, providing more insights into the mechanism of interference between FluA and FluB and the lack of reassortants between them.

Application of a split luciferase complementation assay for the detection of viral protein-protein interactions

Intraviral protein-protein interactions are critical for virus survival in the host. Discovery of such interactions is important to understand molecular mechanisms of viral replication and pathogenesis. The development of a cell-based assay that can be employed to examine systematically viral protein interactions is described. The method, known as the split luciferase complementation assay (SLCA), is based on the principle that N- and C-terminal domains of luciferase alone do not emit luminescence; however, if fused to interacting proteins the two non-functional halves can be brought into close enough proximity through a specific protein-protein interaction to restore the functions of the enzyme and emit detectable light. The well-studied influenza B polymerase acidic protein (PA) and basic protein 1 (PB1) interaction was used as a model system to develop the assay. Consistent with previous studies, a strong PA-PB1 interaction was demonstrated in the assay. The PA-PB1 interaction was also disrupted by single amino acid mutations in the N-terminal domain of PB1 that is responsible for binding PA. The described SLCA is highly specific and easy to perform, and thus may be useful for studying protein-protein interactions in viral diseases.