biostudies-literatureNakatsu SDepartment of Health, Labor, and Welfare of JapanMinistries of Education, Culture, Sport, Science, and TechnologyJapan Agency for Medical Research and DevelopmentHHS | NIH | National Institute of Allergy and Infectious DiseasesJapan Science and Technology AgencyJapan Society for the Promotion of Sciencee01248-16https://www.ebi.ac.uk/biostudies/studies/S-EPMC5013298biostudies-literatureUnknown7(5)The genomes of influenza A and B viruses comprise eight segmented, single-stranded, negative-sense viral RNAs (vRNAs). Although segmentation of the virus genome complicates the packaging of infectious progeny into virions, it provides an evolutionary benefit in that it allows viruses to exchange vRNAs with other strains. Influenza A viruses are believed to package their eight different vRNAs in a specific manner. However, several studies have shown that many viruses are noninfectious and fail to package at least one vRNA. Therefore, the genome-packaging mechanism is not fully understood. In this study, we used electron microscopy to count the number of ribonucleoproteins (RNPs) inside the virions of different influenza A and B virus strains. All eight strains examined displayed eight RNPs mBioComplete and Incomplete Genome Packaging of Influenza A and B Viruses.PMC501329816H06429Sagara HNakatsu SKawaoka YNoda TSakai-Tagawa YSugaya NfalseComplete and Incomplete Genome Packaging of Influenza A and B Viruses.The genomes of influenza A and B viruses comprise eight segmented, single-stranded, negative-sense viral RNAs (vRNAs). Although segmentation of the virus genome complicates the packaging of infectious progeny into virions, it provides an evolutionary benefit in that it allows viruses to exchange vRNAs with other strains. Influenza A viruses are believed to package their eight different vRNAs in a specific manner. However, several studies have shown that many viruses are noninfectious and fail to package at least one vRNA. Therefore, the genome-packaging mechanism is not fully understood. In this study, we used electron microscopy to count the number of ribonucleoproteins (RNPs) inside the virions of different influenza A and B virus strains. All eight strains examined displayed eight RNPs 2016-01-01T00:00:00Z2016 Sep2025-04-26T14:13:00.055Z2019-03-27T02:23:36ZS-EPMC50132982760157510.1128/mBio.01248-16