Assembly of viral membranes: nature of the association of vesicular stomatitis virus proteins to membranes.

To explore the interaction of vesicular stomatitis virus (VSV) proteins with cellular membranes, we have isolated membranes from infected cells that have been radioactively pulse-labeled. We have found conditions of isolation that result in membrane preparation which contain primarily the VSV membrane protein (M) and glycoprotein (G). Both of these proteins are very firmly attached to membranes: conditions known to release peripherally associated membrane proteins from membranes (S. Razin, Biochim, Biophys. Acta 265:241-246, 1972; S. J. Singer, Annu. Rev. Biochem. 43:805-826, 1974; S. J. Singer and G. L. Nicholson, Science 175:720-731, 1972) are ineffective in detaching either the G or the M protein. The results of trypsin digestion of these membrane fractions suggest that the M protein resides primarily on one side, the cytoplasmic side of cellular membranes, whereas the glycoprotein has been transported to the lumen of the membrane vesicle. However, we present evidence that the glycoprotein is transmembranal and that approximately 3,000 daltons of one end of the molecule is on the cytoplasmic side of the membrane. We have also found that undenatured VSV M protein contains a trypsin-resistant core with a molecular weight of 22,000. This region of the M protein is trypsin-resistant regardless of its association with membranes.