Structure of T4 polyheads

Steven, Alasdair C.; Couture, E.; Aebi, Ueli; Showe, Michael K.

doi:10.1016/0022-2836(76)90307-7

Cited by 117 publications

(27 citation statements)

References 30 publications

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“…It appears unlikely from our results that either DNA synthesis or protein cleavage provides the driving force for DNA condensation (3,6,8). However, it also has been suggested that p21-induced cleavage of capsid proteins causes major changes in the surface lattice structure and an increase in head volume (30). If this is the case, the p21 cleavage-induced volume changes are not directly coupled to DNA packaging, as is also suggested by comparison of the sizes of the full and empty cs2O heads (Fig.…”

Section: J and K)mentioning

confidence: 85%

DNA packaging and the pathway of bacteriophage T4 head assembly.

Hsiao¹,

Black²

1977

Proc. Natl. Acad. Sci. U.S.A.

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A cold-sensitive mutation in the structural gene for a minor phage T4 capsid protein (p20) leads to formation of heads containing p20 and cleaved head proteins and empty of DNA. Such heads can be filled with DNA and converted to active phages in vivo upon shift to high temperature. It appears that p20 has two distinct roles in head assembly: first, in construction of the prehead shell (blocked by ts and am mutation) and, second, in DNA packaging (blocked by cs mutation). The latter function is closely associated with gene 17 product, previously known to be required for DNA packaging. Temperature shift studies of cs-s double mutants and other observations allow determination of phage functions required for DNA packaging. Contrary to previous proposals, we find that T4 DNA packaging is not directly coupled to and can follow DNA synthesis, protein cleavage, prehead core removal, and gene 21-mediated cleavage-induced increase in head volume. Our evidence suggests that an altered head assembly pathway exists and that DNA packaging is probably initiated by DNA-capsid (p20) (p23) (5). In this paper we present evidence suggesting that neither of these pathways is correct. The evidence is also against the proposal that filling of T4 heads with DNA depends upon concurrent DNA synthesis (6).These questions are important because they relate to the function of protein cleavage in virus assembly and the unknown mechanism of DNA condensation. It was initially thought that basic DNA-binding internal proteins of the mature head might condense the DNA, but these proteins proved to be nonessential (1, 7). It was then proposed that DNA packaging was coupled to cleavage of core proteins, so that the generation of acidic internal peptide core remnants might cause repulsive collapse to {-like DNA (8, 9). Similarly, packaging could be coupled to exit of core proteins from the prehead in phages lacking protein processing (10). Another general idea is that packaging is coupled to the expansion of the capsid shell which accompanies protein processing and head filling (11, 12).In this paper we characterize a cold-sensitive (cs Fig. 4k) and was not associated with polyhead production, but gave rise to empty head structures (Fig. 1). The phenotype of this cs2O mutation is similar to that of gene 17 mutations. Indeed, the cs20 mutation and gene 17 function appear very closely interrelated because of (i) similar morphological phenotypes (empty head and ghost production); (ii) accumulation of similar sized concatameric T4 DNA (unpublished); (iii) Thin sections of bacteria infected with cs20 at nonpermissive temperature reveal many empty heads in the interior of the cell (Fig. 1). These clearly differ from the protein core-containing membrane-associated Tau-particles which are also seen in small numbers and are known to be intermediates in head formation (2, 19). The cs20 heads appear to be empty of DNA or core material, and to be of roughly the same size as the occasional head fully packaged with DNA seen in growth under slightly le...

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Section: J and K)mentioning

confidence: 85%

DNA packaging and the pathway of bacteriophage T4 head assembly.

Hsiao¹,

Black²

1977

Proc. Natl. Acad. Sci. U.S.A.

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“…The isolation of polyheads has been described (24). The preheads were isolated by differential centrifugation by a similar procedure; details will be described elsewhere (15 (33).…”

Section: Fig 2 Preheads and Polyheads Frommentioning

confidence: 99%

“…The ptg phenotype is probably also based on an alteration in vertex stabilization. Amber and temperature-sensitive mutations in gene 24 have been described as giving rise to 7 particles [since shown to be nearly normal preheads (26)] and polyheads (29). Temperature-sensitive mutants in gene 24, grown at intermediate temperatures, produce small numbers of infectious giant phage (36).…”

Section: Fig 2 Preheads and Polyheads Frommentioning

confidence: 99%

“…2). The membrane attachment vertex (or proximal vertex) is probably also the tail attachment site, because its structure is different from that of the other vertices (18).The form of the T4 prehead is determined by the products of the "head genes," which are sequentially clustered on the genetic map in the order 20, PIP,21,22,23,24 ( The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.…”

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confidence: 99%

“…The length and width of the prehead are determined by the aggregation properties and concentrations of these gene products in the infected cells, as discussed below. 24 (amN65) lysates. Microscopy was carried out as described previously (15) (29,31).…”

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confidence: 99%

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Kinetic factors and form determination of the head of bacteriophage T4.

Showe¹,

Onorato²

1978

Proc. Natl. Acad. Sci. U.S.A.

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The form of the bacteriophage T4 prehead is described by its icosahedral symmetry, its diameter, and its length. We show how each oftheseparameters is regulated during prehead formation and ascribe specific form-determining functions to the prehead proteins. The major protein of the head shell can assemble in several different forms. The structure produced in vivo depends on the rate of synthesis of the major protein relative to the rates of synthesis of minor shell proteins and the major core protein. From our observations, we propose a model for form determination of the prehead and suggest a pathway for the evolution of its prolate shape.The head of bacteriophage T4 has been extensively studied as a model for discovering mechanisms of form determination of biological structures. It is a prolate icosahedron of triangulation number (T) = 13 (1, 2) elongated on its 5-fold axis of symmetry (3), with a length-to-width ratio of 1.37 (4). It is assembled on the Escherichia colh inner membrane as a core-containing prehead (5), which is matured to the finished head by a series of reactions that includes limited proteolysis of capsid and core proteins, expansion of the prehead shell lattice, and packaging of the phage DNA (6). The relatively large size and the prolate shape of the T4 head suggest that the prehead [in which the form is already determined (4)] cannot be produced by simple self-assembly of the shell protein, as is possible with small regular icosahedral viruses (7,8).A number of mechanisms have been proposed (9, 10) to account for form determination in the assembly of large or anisometric virus shells or other structures in which simple selfassembly of identical subunits is not possible (11). They include regulation by a genetically defined "measuring rod" or template, a vernier, and accumulating strain with the addition of subunits. Of these, only the "measuring rod" model, (the determination of the length of tobacco mosaic virus by its RNA) has been experimentally demonstrated (12,13). All of these models depend strongly on specific interactions between the polymerizing subunits, but Wagenknecht and Bloomfield (14) have shown theoretically how the length of linear aggregates might also depend on the concentration of the polymerizing subunits.Recent observations on the role of minor proteins in prehead formation, and on changes in prehead length that depend on subunit concentrations, suggest that kinetic factors as well as specific protein-protein interactions regulate the form of the T4 prehead.The form of the T4 prehead is described by its symmetry (icosahedral), its width, and its length (extension along the 5-fold axis of symmetry). We account for these in the following way. The symmetry is determined by formation of a 5-fold symmetric initiation complex that directs assembly of the shell into closed structures instead of open tubes. The width is determined by the intrinsic curvature of the shell and the diameter of the core that it must enclose. The length can be varied. It is regulated by t...

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