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

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Abstract
The efficient incorporation of influenza virus genome segments into virions is mediated bycis-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.