Control of genomic RNA replication by the nonstructural protein NS2 of influenza A virus.

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The genome RNA segment 8 of influenza A virus encodes two nonstructural proteins, NS1 and NS2. Function of these proteins, in particular for NS2 protein, in viral replication cycle is unknown. We have succeeded to isolate an NS2 mutant. Wa-182, which produced a large amount of defective interfering(DI) particles lacking the PA polymerase gene. In the present study using the NS2 mutant Wa-182 and wild type viruses whose NS2 protein was expressed either at the beginning of infection or at the late phase of infection, we demonstrated (1) that NS2 protein promoted normal replication of genome RNA segments through the suppression of DI-RNA synthesis, (2) that NS2 protein conferred selective packaging of genome RNAs by an intermolecular recognition among RNA segments, and (3) that NS2 protein controlled the initiation of genome RNA replication by the regulation of cRNA synthesis. These observations indicate that the NS2 protein functions to be a regulator in multiple steps of viral growth cycle.