Morphogenesis of bacteriophage phi 6: a presumptive viral membrane precursor

Bacteriophage phi 6 has a lipid- and protein-containing membrane as its outer covering. Two phi 6-coded proteins are known to be required to produce enveloped phage particles: one is P9, the major phi 6 membrane structural protein, and the other is P12, a nonstructural protein without which membrane fails to assemble around phage nucleocapsids. A particle containing phospholipid, P9, and two minor phi 6 membrane proteins has been found in cells pulse labeled with protein precursors at late times after infection. The P9 particle can be chased into phage and is dependent on active P12 for its formation. Models are presented in which the role of the P9 particle in phi 6 membrane assembly is discussed.