Membrane interaction of influenza virus M1 protein

The M1 protein of influenza virus is thought to make contact with the cytop lasmic tails of the glycoprotein spikes, lipid molecules in the viral membr ane, and the internal ribonucleoprotein particles. Here we show electron mi crographs of negatively stained virus particles in which M1 is visualized a s a BO-A-long rod that touches the membrane but apparently is not membrane inserted. Photolabeling with a membrane restricted reagent resulted in labe ling of the transmembrane region of haemagglutinin but not of M1, also sugg esting that most of M1 is not embedded into the hydrophobic core of the vir al membrane. Finally, in vitro reconstitution experiments using soluble M1 protein and synthetic liposomes or Madin-Darby canine kidney cell membranes suggest that M1 can bind to negatively charged liposomes and to the cellul ar membranes and that this binding can be prevented under high-salt conditi ons. Although none of these experiments prove that there does not exist a m inor fraction of M1 that is membrane inserted, it appears that most of M1 i n the virus is membrane associated through electrostatic interactions. (C) 2000 Academic Press.