Structure of the bacteriophage P2 tail

Abstract

Analysis of bacteriophage P2 particle proteins by SDS gel electrophoresis indicates that at least six proteins are present in the tail. A tail protein of 71,000 daltons has been identified as the product of the H gene, and a tail protein of 94,000 daltons has been tentatively identified as the T gene product. The T protein appears to be stabilized by the E gene product. The major tail proteins, of 46,000 and 19,600 daltons, are missing from cells infected with an F amber mutant, but not from cells infected with amber mutants in any of the genes downstream from F. These two proteins are designated F I and F II, respectively. We propose that one of these proteins is coded for a gene adjacent to F which has not yet been defined by mutation. On the basis of their relative proportions in the phage and their molecular weights, we propose that F I and F II are the tail sheath and tube proteins, respectively, and that the T protein may be a tail-fiber component. High-resolution (minimal beam exposure) electron microscopy has revealed the structure of the contractile P2 tail in greater detail. At the head-proximal end of free tails are two disclike structures of different thickness and diameter. In preparations of whole phage, only the thinner of these discs is seen to lie outside the phage head (at the head-tail junction). We, therefore, presume that the thicker disc lies inside the head. At the distal end of the tail is a small, slender spike, and six tail fibers which are composed of two subsections. Electron microscopic examination of cells infected with different tail amber mutants indicates that the tail genes R and S are involved in determining tail length, since these mutants produce giant tails and giant tail sheaths, respectively.