The N Terminus of the Influenza B Virus Nucleoprotein Is Essential for Virus Viability, Nuclear Localization, and Optimal Transcription and Replication of the Viral Genome

Abstract

The multifunctional NP of influenza viruses has roles throughout the viral replication cycle; therefore, it is essential for virus viability. Despite high levels of homology between the NP of influenza A and B viruses, the NP of influenza B virus contains an evolutionarily conserved 50-amino-acid N-terminal extension that is absent from the NP of influenza A viruses. In this study, we show that this N-terminal extension is essential for virus viability, and we confirm and expand upon recent findings that this region of BNP is required for nuclear localization of the protein. Furthermore, we demonstrate for the first time that the N terminus of BNP is involved in regulating viral mRNA transcription and replication of the viral genome. As the NP of influenza A virus lacks this N-terminal extension, these viruses may have evolved separate mechanisms to regulate these processes.