Membrane assembly from purified components. II. Assembly of M13 procoat into liposomes reconstituted with purified leader peptidase.

The major coat protein of coliphage M13 is an integral protein of the E. coli plasma membrane prior to its assembly into new virus particles. It is generated from its precursor, procoat, by a membrane-bound leader peptidase. We now describe the reconstitution of a highly purified preparation of this enzyme into vesicles of E. coli phospholipids. These vesicles bind procoat made in vitro and procoat isolated from in vitro synthesis. Both the crude and the purified substrates were converted post-translationally to coat protein. A significant proportion of the coat protein becomes inserted into the vesicle bilayer, with the N terminus facing the vesicle interior and the C terminus exposed to the external medium. These results strongly suggest that highly purified leader peptidase from E. coli and phospholipids are the only components necessary to mediate the binding, processing and insertion of this integral membrane protein.