INFLUENZA-VIRUS HEMAGGLUTININ AND NEURAMINIDASE GLYCOPROTEINS STIMULATE THE MEMBRANE ASSOCIATION OF THE MATRIX PROTEIN

We have analyzed the mechanism by which the matrix (M1) protein associ ates with cellular membranes during influenza A virus assembly, Intera ction of the M1 protein with the viral hemagglutinin (HA) br neuramini dase (NA) glycoprotein was extensively analyzed by using wild-type and transfectant influenza viruses as well as recombinant vaccinia viruse s expressing the M1 protein, HA, or NA. Membrane binding of the M1 pro tein was significantly stimulated at the late stage of virus infection . Using recombinant vaccinia viruses, we found that a relatively small fraction (20 to 40%) of the cytoplasmic M1 protein associated with ce llular membranes in the absence of other viral proteins, while coexpre ssion of the HA and the NA stimulated membrane binding of the M1 prote in, The stimulatory effect of the NA (>90%) was significant and higher than that of the HA (>60%). Introduction of mutations into the cytopl asmic tail of the NA interfered with its stimulatory effect, Meanwhile , the HA may complement the defective NA and facilitate virus assembly in cells infected with the NA/TAIL(-) transfectant. In conclusion, th e highly conserved cytoplasmic tails of the HA and NA play an importan t role in virus assembly.