Host-range determinants on the PB2 protein of influenza A viruses control the interaction between the viral polymerase and nucleoprotein in human cells

The transcription/replication activity of ribonucleoproteins derived from influenza A primary isolates of human (A/Paris/908/97) or avian origin (A/Mallard/Marquenterre/MZ237/83, A/Hong Kong/156/97) was compared upon reconstitution in mammalian or avian cells, using viral-like reporter RNAs synthesized under the control of the human and chicken RNA polymerase I promoters, respectively. In avian cells, transcription/replication activities were in the same range with all ribonucleoproteins tested. In human cells, ribonucleoproteins derived from A/Mallard/Marquenterre/MZ237/83 showed reduced transcription/replication activity and reduced NP binding to the PB1–PB2–PA complex (P) or to the isolated PB2 subunit, as compared to the ribonucleoproteins derived from A/Paris/908/97. Both defects were restored when PB2 residue Glu-627 was changed to a Lys. Ribonucleoproteins derived from the human A/Hong Kong/156/97 H5N1 isolate showed efficient NP–P interaction in human cells, and high levels of activity which were determined mostly by the PB2 and PA proteins. Our data suggest that PB2 might play a pivotal role in molecular interactions involving both the viral nucleoprotein and cellular proteins.