Precursors of the T4 internal peptides

Formation of the prohead core of bacteriophage T4 was not dependent on shell assembly. In mutant infections, where the production or assembly of active shell protein was not possible, naked core structures were formed. The particles were generally attached to the bacterial inner membrane and possessed defined prolate dimensions. The intracellular yield varied between 15 and 71% of a corresponding prohead yield and was dependent on the temperature of incubation. The products of genes 21 and 22 were found to be essential for in vivo core formation, whereas those of genes 20, 23, 24, 31, and 40, as well as the internal proteins I to III, were dispensable. Bacteriophage T4 has attracted in the past years considerable attention as a model for viral morphogenesis and its underlying principles. The mechanisms of form and size determination in head and tail formation are of general interest (5, 7, 34). The study of the T4 assembly process has led to the formulation of a fundamental principle: the subunits of a precursor particle undergo sequential changes into specific conformations which either induce the ability to interact with and to bind to a new type of subunit or activate specific chemical events within the particle (e.g., proteolysis) (20, 21). The major elements of bacteriophage T4, the head, the tail, and the tail fibers, are built in independent assembly pathways before joining to form the mature virion

Section: Discussionmentioning

confidence: 99%

Formation of the prohead core of bacteriophage T4 in vivo

Traub¹,

Maeder²

1984

“…The specific mutants used are listed in Table 1. Stocks were prepared as previously described (9). The designation of multiple mutants follows the nomenclature of Laemmli et al (14).…”

mentioning

confidence: 99%

Isolation and characterization of bacteriophage T4 mutant preheads

Onorato¹,

Stirmer²,

Showe³

1978

To determine the function of individual gene products in the assembly and maturation of the T4 prehead, we have isolated and characterized aberrant preheads produced by mutations in three of the T4 head genes. Mutants in gene 21, which codes for the T4 maturation protease, produce rather stable preheads whose morphology and protein composition are consistent with a wild-type prehead blocked in the maturation cleavages. Mutants in gene 24 produce similar structures which are unstable because they have gaps at all of their icosahedral vertices except the membrane attachment site. In addition, greatly elongated "giant preheads" are produced, suggesting that in the absence of P24 at the vertices, the distal cap of the prehead is unstable, allowing abnormal elongation of both the prehead core and its shell. Vertex completion by P24 is required to allow the maturation cleavages to occur, and 24-preheads can be matured to capsids in vitro by the addition of P24. Preheads produced by a temperaturesensitive mutant in gene 23 are deficient in core proteins. We show that the shell of these preheads has the expanded lattice characteristic of the mature capsid as well as the binding sites for the proteins hoc and soc, even though none of the maturation cleavage takes place. We also show that 21-preheads composed of wild-type P23 can be expanded in vitro without cleavage.

“…During formation of the prehead, an icosahedral shell of gp23 (the product of gene 23), which is the main essential structural component of the mature capsid (14), is assembled around a scaffold-like structure termed the morphogenetic core. The principal essential protein of this core is gp22, although several other proteins are also components of the core structure (18,28). In the process of capsid maturation, the core is proteolytically degraded (19).…”

mentioning

confidence: 99%

Genetic studies on capsid-length determination in bacteriophage T4. I. Isolation and partial characterization of second-site revertants of a gene 23 mutation affecting capsid length

Doherty¹

1982

The T4 mutation ptgl9-80 affects the mechanism of capsid-length determination. It is located in gene 23, which encodes the major structural protein of the capsid. The mutation results in the production of abnormal-length capsids in high frequencies. This paper describes the isolation and partial characterization of second-site revertants of ptgl9-80. In the course of their analysis, it was discovered that ptgl9-80 is itself a double mutation consisting of a gene 23 mutation (ptgl9-80c), which causes the morphogenetic defect, and a suppressor mutation located near the lysozyme gene. Phenotypic characterization of nine pseudo-wild-type revertants of this double mutation revealed that these revertants all produced lower frequencies of abnormal capsids than did ptgl9-80. Seven of these revertants were shown to contain two suppressor mutations, one mapping in or near gene 22 and one mapping in or near gene 24. Both mutations were required for suppression. These suppressors displayed no discernible phenotype in the absence of ptgl9-80c.