Measles Virus Assembly within Membrane Rafts

During measles virus (MV) replication, approximately half of the internal M and N proteins, together with envelope H and F glycoproteins, are selectively enriched in microdomains rich in cholesterol and sphingolipids called membrane rafts. Rafts isolated from MV-infected cells after cold Triton X-100 solubilization and flotation in a sucrose gradient contain all MV components and are infectious. Furthermore, the H and F glycoproteins from released virus are also partly in membrane rafts (S. N. Manié et al., J. Virol. 74:305-311, 2000). When expressed alone, the M but not N protein shows a low partitioning (around 10%) into rafts; this distribution is unchanged when all of the internal proteins, M, N, P, and L, are coexpressed. After infection with MGV, a chimeric MV where both H and F proteins have been replaced by vesicular stomatitis virus G protein, both the M and N proteins were found enriched in membrane rafts, whereas the G protein was not. These data suggest that assembly of internal MV proteins into rafts requires the presence of the MV genome. The F but not H glycoprotein has the intrinsic ability to be localized in rafts. When coexpressed with F, the H glycoprotein is dragged into the rafts. This is not observed following coexpression of either the M or N protein. We propose a model for MV assembly into membrane rafts where the virus envelope and the ribonucleoparticle colocalize and associate.