Influenza A packaging mutants
The influenza A virus (IAV) genome consists of eight unique viral RNAs (vRNAs) organized as ri-bonucleoproteins (vRNPs). In the majority of wild-type virus particles, these eight vRNPs are coor-dinately packaged as a (7+1) complex. Assembly and packaging of this generic genomic complex is thought to be controlled by packaging signals in all vRNAs, a concept based largely on the fact that mutations in packaging signals can reduce multiple vRNAs in the virion population. However, the associated changes in the architecture and composition of the (7+1) complex remain unclear. Here, we show that an IAV mutant with reduced packaging of four vRNAs generates three major classes of virions that either lack all vRNPs, contain incomplete genome complexes with one to seven vRNPs, or carry complete (7+1) complexes. In addition to the generic (7+1) complex, we also find atypical (7+1) complexes that contain identical copies of efficiently packaged vRNAs. Thus, a diverse landscape of genome complexes underlies unbalanced vRNA packaging. Our re-sults not only confirm the critical role of packaging signals in the formation of the generic (7+1) complex, but also support the emerging concept that its composition may vary when one or more vRNAs are unavailable for packaging.