The cytoplasmic tail of the neuraminidase protein of influenza A virus does not play an important role in the packaging of this protein into viral envelopes.

We have rescued a transfectant influenza virus, NA/TAIL(-), whose neuraminidase (NA) protein lacks the predicted cytoplasmic tail. The virus was attenuated (one log10 reduction) both in tissue culture and in mouse lungs. Attenuation correlated with a 50% reduction of the level of NA in infected cells and levels of incorporation of the tail-less NA protein into viral particles paralleled that in infected cells. This result indicates that the signal for packaging of the NA protein into the viral envelope is not located in its cytoplasmic domain.