In part 1 of this paper ( I ) we give evidence that the P23-capsoid of 7-particles is transformed in situ i n t o the P23*-capsid of' normal phage. Using t h e polymorphism of phage T4, we have chosen polyheads as representative of P 2 3 assemblies and giant phages as representative of P23* assemblies in order t o study their surface crystals by optical filtration of micrographs. We found for polyheads a lattice constant of 1 I 2 a with the typical hexameric, ringlike capsomer and for t h e giants a lattice constant of 124 a with quite a different capsomer morphology, of t h e t y p e (h+l). From the stoichiometry of t h e proteins composing the normal capsid we conclude that the prototner is a single P23* molecule and that the minor capsidproteins must be in singular positions on t h e surface lattice o r on t h e polyhedral head (center of capsomers, vertices, o r basal part).We extrapolate the findings on the giant head to t h e normal head and give a geometric model which is consistent with 1 , I 00 molecules o f P23* per capsid.We discuss t h e part of form inheritance contrihuted by P23 and t h e other formgiving gene products and give evidence that morphologic characters are t h e result of pairs of a reaction chain of interacting gene products. The example we give is the giant head produced by a t s mutant in gene 2 4 at 3h'C.

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Asynchroneous T4 phage head maturation includes the step of P23 cleavage: P23 of head-related r-particles is cleaved into P23* of capsids with a conservative mode of transformation as evidenced by "heavy" labeling in temperature shift-down experiments with mutant 24 (tsL90). Assuming a subunit pool, data indicate in situ cleavage on individual precursor particles. The interpretation becomes less interesting when assuming a compartmentation of the membrane surface; this hypothesis is not ruled out. INTRODUCTIONExperimental results described in a previous paper (1) suggest that 7-particles produced by a phage T4 temperature-sensitive (ts) mutant in gene 24 can be matured into T4 phage heads after shift t o permissive temperature (temperature shift-down). 7-particles produced in 21 -infected cells, which are morphologically indistinguishable, were found not t o be maturable. When observed intracellularly by thin sections (Fig. l), r-particles are very characteristic (3). A core is surrounded by a capsoid; like the mature head, they are prolate but significantly less angular than the latter. In both length and width, 7-particles are about 20% smaller; the 7-capsoid is visibly thicker than the mature capsid ( Fig. 1). 7-capsoids contain the uncleaved product of gene 23 (4), which has a molecular weight of 59,000 daltons, while the matured capsid is made with the cleaved P23 (P23*) (4-7) with a molecular weight of 47,SOOQlW is determined by amino acid composition A culture of Escherichia coli BE was infected and superinfected with a multiplicity of 5 with T4.24 (am N65) or T4 wild type. Sixty min after infection the cells were prefixed with formaldehyde, then concentrated by centrifugation and osmium fixed under conventional R-K conditions (2) followed by embedding. 7-particles (a) characterized by their smaller dimensions (in length and width about 20%), by the presence of an internal core and by a thicker membrane when compared to the normal phage head (b). The 7-particles have their long axis perpendicular to the inner surface of the cell membrane. Polyheads (elongated structures) and ribosomes (dark dots) can also be seen (a). tribution is not known and hence not interpretable (170,000 X). Electron micrographs by J. van den Broek.Thickness measurements of the capsids and capsoids are not meaningful, as long as the stain disby A. Tsugta; to be published). For normal phage multiplication Laemmli (4) has shown that P23 is converted into P23* in roughly 2-3 min, which is about one-third to one-half of the total time needed for building a T-even head (8). In the present paper we will demonstrate that the uncleaved P23 is organized in the form of a precursor particle, in which, later, the conversion of P23 t o P23* is conservative. Our experimental controls are mainly designed t o check the possibility of a labile P23-particle, which after dissociation would replenish a P23 subunit pool. Experiments to test the compartmentation hypothesis are difficult to design, and so we limit ourselves to a discussion of some of its ...

A study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature-sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L-canavanine followed by an Larginine chase in the growth medium. All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near-hexagonal surface net, lattice constant 129.5 A, folded into a left-handed T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild-type T-even phage capsids is their abnormally elongated tubular part. A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are identical but differ from T2L: The T4D capsomere has a complex (6 + 6 + 1)-type morphology, whereas the T2L has a simple 6-type. T2L phage, however, lack two capsid proteins, "soc" and "hoc", present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage. Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.