Purification and characterization of the major protein and the terminator protein of the bacteriophage λ tail

Abstract

Two proteins of the tail of bacteriophage λ were purified in an active form and characterized for the study of phage assembly. The terminator protein (product of gene U), which stops the polymerization of the major tail protein at the correct tail length, was purified from crude lysates. It exists as a globular monomer of 16,000 daltons in the absence of magnesium ions and as a ring-like hexamer in the presence of 20 m M MgSO 4. It is a very acidic protein poor in lysine and lacking cysteine residues. Its secondary structure is rich in β-sheet and relatively poor in α-helix. Experiments using its antibody show that it is located at the proximal end of the tail. The major tail protein (product of gene V) was purified from dissociated tails or phage ghosts. This preparation was indistinguishable from the unassembled major tail protein in tail-defective lysates with respect to various properties except that the in vitro complementation activity was significantly lower. The gene V product consists of a polypeptide chain of about 25,000 daltons, which is rich in valine and threonine and which has no cysteine and no or an extremely small amount of histidine. Its secondary structure contains a large amount of random-coil, a relatively small amount of β-sheet, and very small amounts of α-helix. In solution it exists in a monomer-dimer equilibrium, and polymerizes only in the presence of the initiator for its assembly. The antibody against the major tail protein attaches all over the tubular part but not to the basal part of the tail.