ASSEMBLY OF TAIL OF BACTERIOPHAGE T4

[摘要] The formation of bacteriophage T4 was studied by characterizing the phage components accumulating in cells infected[long dash]under restrictive conditions[long dash]with mutants blocked at different stages of the assembly process. Three structures which appear to be intermediates in tail assembly isolated by centrifugation baseplates (S20,w[image]80 s) core-baseplates (S20 w [image]80 s) and core-baseplates with surrounding sheath (S20 w=130 s). The functions of genes 18, 48 and 54 are required for the conversion of the baseplate to the core-baseplate. The functions of genes 3, 15 and 18 are required for the formation of the sheath. Gene 18 codes for a major structural protein of the sheath. Genes 3 and 15 specify products required for the stabilization and completion of the sheath. Tail assembly is sequenced; the baseplate is completed 1st and the core forms on the baseplate. The gene 18 product polymerizes on the core-baseplate, and then the 3 and 15 gene products fix the sheath subunits in the polymerized form. After sheath formation, a segment appears to be added to the core at the terminus of the sheath permitting subsequent attachment of the head. The tail fibers attach only after the particle formed by head-tail union was acted upon by the gene 9 product. Particles not acted upon by the gene 11 or 12 product adsorb to but do not kill bacteria. Electron microscopic observations on the state of phage heads in mutant lysates are presented. Mutations in 3 genes result in the accumulation of head membranes without DNA. Phage heads and phage tails are formed independently of each other.