Organization and function of the tail of bacteriophage T4: II. Structural control of the tail contraction

Abstract

The interaction of proteins, during their operation in the mature T4 bacteriophage particle, was studied by examining the function of various mutant phage particles incorporating genetically altered protein(s) or those that lack the component protein(s). Thus, the contraction behavior of the tail of the phage was studied by heating phage particles which carried various combinations of heat-sensitive ( hs) mutations and structural defects produced by amber ( am) mutations. The following phenomena were observed: 1. (1) Elimination of the long tail fibers from the viral particle completely suppressed tail contraction in many situations, provided the phage particle retained protein P9 ‡ ‡ Abbreviations used: P before the number of a gene indicates the product of that gene; am, amber; hs, heat sensitive. When necessary, the gene name is inserted between square brackets before the isolate number of a mutant; thus, hs[6]Y122 should read as hs mutant Y122 in gene 6. . 2. (2) Elimination of P12, the short tail fibers, induced tail contraction after heat treatment at 55 °C, which does not affect intact phage particles. 3. (3) Heat denaturation of the carboxyl terminus of the short tail fiber inhibited the process of tail contraction. The inhibition was relaxed by superimposed denaturation of P5, as indicated by the behavior of double mutants hs in genes 5 and 12. 4. (4) Major constituent proteins of the tail, including P12 and P9, were conserved during tail contraction. Based on these findings, a possible model of the baseplate was constructed in which P6, P7, P8, P10, P25, P27 and P29 were visualized to constitute one functional unit acting as the skeleton of the baseplate whose hexagon-hexagram transition was controlled by “the outer proteins” which included P5, P9, P11 and both the short and long tail fibers.