Incorporation of influenza A virus genome segments does not absolutely require wild-type sequences

The efficient incorporation of influenza virus genome segments into virions is mediated by cis-acting regions at both ends of the viral RNAs. It was shown previously that nt 16-26 at the 3' end of the non-structural (NS) viral RNA of influenza A virus are important for efficient virion incorporation and that nt 27-56 also contribute to this process. To understand further the signalling requirements for genome packaging, this study performed linker-scanning mutagenesis in the latter region and found that nt 27-35 made an appreciable contribution to the efficient incorporation of the NS segment. An NS vRNA library was then generated composed of an RNA population with randomized nucleotides at positions 16-35 such that the virus could select the sequences it required for virion incorporation. The sequences selected differed from the wild-type sequence and no conserved nucleotides were selected. The ability of non-wild-type sequences to function in this manner indicates that the incorporation of influenza A virus genome segments does not absolutely require specific sequences.