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 selectiv ely enriched in microdomains rich in cholesterol and sphingolipids called m embrane rafts. Rafts isolated from MV-infected cells after cold Triton X-10 0 solubilization and flotation in a sucrose gradient contain all MV compone nts and are infectious. Furthermore, the H and F glycoproteins from release d virus are also partly in membrane rafts (S, N, Manie 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 a ll of the internal proteins, M, N, P, and L, are coexpressed, After infecti on with MGV, a chimeric MV where both H and F proteins have been replaced b y vesicular stomatitis virus G protein, both the M and N proteins were foun d enriched in membrane rafts, whereas the G protein was not. These data sug gest that assembly of internal MV proteins into rafts requires the presence of the IMV genome. The F but not H glycoprotein has the intrinsic ability to be localized in rafts, When coexpressed with F, the H glycoprotein is dr agged 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 associa te.