E proteins of bacteriophage P22. I. Identification and ejection from wild-type and defective particles

Of the nine proteins found in the virion of phage P22, four are ejected into the cell after adsorption. The four ejected proteins, termed E proteins, are gp16, gp20, gp26, and gp7. This was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radioactively labeled phage that had been adsorbed to cells and then eluted off the surface with distilled water. Phage particles that lack gp7 (7- particles) or gp20 (20- particles) successfully eject all their E proteins. The 16- particles do not eject gp7. Analysis of phage ghosts showed that they lack gp16, gp20, and gp7, but they have gp26 in close to normal quantities. Our results suggest roles for gp16 and gp26 in DNA and E protein ejection. All four E proteins are possible candidates for roles in helping the phage DNA cross the plasma membrane.