Membrane-associated assembly of M13 phage in extracts of virus-infected Escherichia coli.

Assembly of coliphage M13 is known to occur as the viral DNA crosses the cytoplasmic membrane, shedding its virus-coded DNA unwinding protein and acquiring from the membrane approximately 2400 copies of the major coat protein. Conditions are described in which extracts of M13-infected E. coli and membranes prepared from such extracts will support virus assembly at a rate equivalent to that of intact cells. Extracts prepared from cells infected with temperature-sensitive M13 mutants in genes 1, 3, 4, or 5 are temperature-sensitive in this cell-free assembly reaction. Phage assembly in vitro requires magnesium and as yet an unidentified heat-stable cofactor of low molecular weight. The rate of virus assembly is approximately linear with respect to extract concentration over a 10(4)-fold range, consistent with the observation that the entire M13 assembly activity copurifies with the cell membrane fraction.