The NB protein is an integral component of the membrane of influenza B virus.

The results of biochemical and immunoelectron microscopic studies provide evidence that the NB protein is an integral component of the influenza B virion. Its glycosylation and orientation in the membrane were shown to be equivalent to that of NB in the plasma membrane of virus-infected cells. Sensitivity to proteinase K showed that the N terminus is exterior to the virion and gold immunolabelling of freeze-fractured replicas showed that the C terminus is located in the interior of the virion. The similarities between NB of influenza B and M2 of influenza A viruses in structural features, their presence in the virion and possession of an ion channel activity suggest that, by analogy with the M2 protein, NB may also have a role in virus entry.