Migration of influenza virus-specific polypeptides from cytoplasm to nucleus of infected cells

Previous studies have shown that various influenza virus polypeptides are associated with the infected cell nucleus. To clarify the pattern of distribution of influenza virus-specific polypeptides between nucleus and cytoplasm in infected cells and to gain further information concerning functions of influenza virus replication occurring in the host cell nucleus, we have used high-resolution pulse-labeling experiments and detailed ultrastructural examination of purified preparations of nuclei. In addition to NP and NS 1, both P 1 and P 2 associate preferentially with the nucleus, while P 3 and NS 2 remain in the cytoplasm. The viral M protein is seen in nuclear fractions only when these fractions are significantly contaminated by plasma membrane. The preferential association of P 1 and P 2 with nuclei suggests that these proteins, in conjunction with NP and NS 1, are involved in specific functions which may include viral transcription, while P 3 and NS 2 are involved in a distinct role in the cytoplasm.