Ultrastructural and functional analyses of recombinant influenza virus ribonucleoproteins suggest dimerization of nucleoprotein during virus amplification

Influenza virus ribonucleoproteins (RNPs) were reconstituted in vivo from c loned cDNAs expressing the three polymerase subunits, the nucleoprotein (NP ), and short template RNAs. The structure of purified RNPs was studied by e lectron microscopy and image processing. Circular and elliptic structures w ere obtained in which the NP and the polymerase complex could be defined, C omparison of the structure of RNPs of various lengths indicated that each N P monomer interacts with approximately 24 nucleotides, The analysis of the amplification of RNPs with different lengths showed that those with the hig hest replication efficiency contained an even number of NP monomers, sugges ting that the NP is incorporated as dimers into newly synthesized RNPs.