[Structure, function and regulation of expression of influenza virus matrix M1 protein].

The M1 protein of influenza virus regulates the bi-directional transport of ribonucleoprotein (RNP) into and out of the nucleus. At the beginning of infection, the incoming RNP is transported into the nucleus only after detachment from M1, where RNP is involved in transcription/replication of the viral genome. In the late stage of infection, M1 inhibits viral RNA polymerase activity by binding to RNP, which may be a signal for RNP-transport from the nucleus to the cell surface. Finally, M1 mediates the association of RNP with viral envelope glycoproteins on the inner surface of the cytoplasmic membrane, which then promotes the virion formation and budding. Thus, M1 is a multi-functional protein that plays important roles in various steps of virus replication.