DISTAL HALF OF THE TAIL FIBER OF BACTERIOPHAGE-T4 - RIGIDLY LINKED DOMAINS AND CROSS-BETA STRUCTURE

The tail fibre of bacteriophage T4 is a structure about 1500 Å long and 30 to 40 Å thick with a kink in the middle dividing it into proximal and distal halves. We have studied the distal half fibre, which is the product of five phage genes. In crude lysates the half fibre forms ordered aggregates, which show characteristic banding patterns when examined in the electron microscope by negative staining. Analysis of the packing of half fibres in the various types of aggregate has enabled us to propose and test a model for the morphology of the half fibre. This consists of a series of rigidly linked stain-excluding globular domains, spaced regularly along the proximal 620 Å of the half fibre with a thinner region about 195 Å long at the distal tip of the fibre. X-ray diffraction and electron diffraction from unstained clumps of purified aggregates both give a strong ring at a spacing of 1 4.7 A ̊-. In the electron diffraction pattern the ring shows marked orientation in a direction corresponding to the axis of the tail fibre, suggesting that it arises from a cross-β fold, in which the polypeptide chain runs transversely to the axis of the fibre. © 1979.