Possibility to Detect Reproducibly some 5-10 Å Conformational Differences by Conventional Techniques: Physiologically Defined Lattice Transformations in Bacteriophage T4

Form determination of the heads of bacteriophages

The shape of the DNA-containing heads of many bacteriophages is not only determined by the properties of the protein subunits which build the shell (capsid) but also by the scaffolding core which is a transient structure of the prohead. The form-determining properties of the scaffolding proteins have been characterized by genetic methods based on conditional mutants and site-directed mutagenesis. The mechanism of form determination has been studied by in vitro assembly experiments. The theoretical background is discussed and different models for mechanisms of form determination are considered. Definitive decisions about the validity of a model is still limited by the difficulty of obtaining unambiguous answers on the stoichiometry and the fine structure of the scaffold because of their high instability.

Head maturation pathway of bacteriophages T4 and T2. V. Maturable epsilon-particle accumulating an acridine-treated bacteriophage T4-infected cells

A maturable head-related particle of bacteriophage T4 has been identified and characterized. This epsilon-particle has the same size as the prehead, but its shell is made of the cleaved product of gene 23 (gp23*). It contains internal matter, most likely the processed core proteins, which is lost or modified by experimental manipulations. It accumulates, together with partially filled ("grizzled") heads, in T4 infected cells that are treated with 9-aminoacridine. On sections of "well-preserved" cells the epsilon-particles are not identifiable with certainty; a more or less empty breakdown product of them becomes visible when cytoplasmic leakage is induced. The number of particles per cell is then in agreement with the biochemically and with the number of particles counted in lysates. Morphologically and biochemically, the isolated epsilon-particles closely resemble the empty small particles of 17- -infected cells described in previous papers of this series. Both are composed of gp23* and are still unexpanded, so that they are not yet able to bind the minor head proteins soc and hoc. We discuss the possibility of the epsilon-particle being an intermediate on the normal T4 wild-type head maturation pathway.