A novel function of the N-terminal domain of PA in assembly of influenza A virus RNA polymerase.

Transcription and replication of the negative-sense single-stranded influenza A virus genomic viral RNA are catalyzed by the viral RNA polymerase, which is a trimeric complex encoded by the three largest segments of the influenza virus genome: PB1, PB2, and PA. Numerous studies of the trimeric polymerase complex assembly have substantially contributed to current understanding of influenza virus replication. However, the dynamics of spatial and temporal macromolecular interactions involving virus and host proteins during the formation of the trimeric polymerase complex (PA-PB1-PB2) are still not completely understood. In this study, bimolecular fluorescence complementation (BiFC) and Raster image correlation spectroscopy (RICS) were applied to monitor the interactions between PB1, PB2, and PA. The BiFC probes of PA-PB1 and PB1-PB2 could monitor the trimeric polymerase complex as well as the binary complex. Furthermore, the C-terminal domain of PA (PAC) promoted interaction between PB1 and PB2 in the cytoplasm and that the N-terminal domain of PA (PAN) inhibited the aberrant trimeric complex formation and assembly of higher-order oligomers induced by PAC in the cytoplasm. Taken together, these results revealed a novel function of PAN in the formation of the trimeric polymerase complexes of influenza A virus.