Assembly Mechanisms

HSV-1 and T4 are by far the best understood of the large viruses and their assembly processes may provide pointers to some of the mechanisms likely to occur in other virus families. In both HSV-1 and T4, the first product of assembly is not the capsid described above but rather a precursor, the procapsid. The formation of procapsids and their role in the capsid assembly pathway have long been known in T4 (see Black et al, 1994). However, in HSV-1, procapsids have been described only relatively recently. Although they were initially identified as the products of in vitro capsid assembly experiments (Newcomb et al, 1994), their role in infected cells is now firmly established (Church and Wilson, 1997 Newcomb et al, 2000 Preston et al, 1983 Rixon and McNab, 1999). Procapsids are formed by polymerization of capsid shell proteins around an internal structure called the scaffold. The scaffold has a number of possible functions but a major purpose is to determine the size and assure the fidelity of the capsid shell (see Fane and Prevelige, This volume). This function is likely to be particularly important for large capsid shells, where the possibility of incorrect interactions is multiplied by the increased number of subunits involved. 

Assembly studies have shown that the HSV-1 portal protein is not required to initiate formation of otherwise normal capsids (Newcomb et al, 1996, 1999 Tatman et al, 1994 Thomsen et al, 1994). However, the presence of single copies of the portal complex in mature capsids (Newcomb et al, 2001) strongly suggests that, as in T4, this is the normal pathway of assembly. 

In both HSV-1 and T4, the procapsids are structurally distinct from typical capsids. This is particularly evident in T4, where maturation involves head expansion, which is accompanied by angularization of the capsid shell (Black et al, 1994). Although maturation of the HSV-1 procapsid does not involve a major size increase, it does alter the shape from spherical to polyhedral (Trus et al, 1996) and is accompanied by changes to the antigenicity of the capsid surface (Gao et al, 1994). In both T4 and HSV-1, maturation has a great effect on the stability of the particles as in both cases mature capsids are resistant to disruption whereas procapsids rapidly dissociate when exposed to fairly mild assaults (Newcomb et al, 1996 Steven et al, 1992 van Driel, 1977). 

The structure of the T4 procapsid has not yet been analyzed in detail but that of HSV-1 has been solved to 18-A resolution (Newcomb et al, 

2000) (Fig. 5). This has revealed a number of features that differentiate the procapsid from the capsid and emphasize the similarities between its assembly pathway and that of certain tailed bacteriophages. The overall dimensions of the HSV-1 procapsid are similar to those of the mature capsid, and the capsid shell contains recognizable pentons, hexons, and triplexes organized in the same T=16 symmetry (Trus et al, 1996). 

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These are Osually mineral oils of medium or low viscosity, which contain specific coirrorion inhibitors arid.anti-Qxidants In spite of the relatively low protective properties of the fluid films, which are not nearly so great as those, Of the previouriy described solid films, these materials have an established field of useon the internal surfaces of tririks and assembled mechanisms, and where solid material or solvent cannot be tolerated. ... 

Deming TJ (2005) Polypeptide hydrogels via a unique assembly mechanism. Soft Matter 1 28-35... 

Flexibility of pattern formation may well be the consequence of self-assembly mechanisms acting upon digital information such as that... 

The diversity of the GABAa subunits (Figure 3.2d) is reflected in a very complex pharmacology. Expression of the subunits in heterologous systems shows that the combinations a, (3, and y can yield functional receptors, indicating that the limitation in subunit combination is defined by expression levels and most likely cell-dependent assembly mechanisms also. The pj to p3 subunits mainly co-assemble with each other to form the GABAC receptors. 

In the near future, we wish to extend kinetics experiments to other synthesis of mesoporous materials, in order to determine how the self-assembly mechanisms are changing with respect to the type of synthesis. 

Plants have the ability to assemble immunoglobulin heavy chains and light chains to form full-length antibodies very efficiently [24]. In mammalian plasma cells, the assembly mechanism is only partially understood. The immunoglobulin light and heavy chains are synthesized as precursor proteins, and signal sequences direct... 

Herrmann, H. and Aebi, U. Intermediate filaments molecular structure, assembly mechanism, and integration into functionally distinct intracellular Scaffolds. Annu. Rev. Biochem. 73 749-789, 2004. 

From the Polymorphism of Amyloid Fibrils to Their Assembly Mechanism and Cytotoxicity... 

FROM THE POLYMORPHISM OF AMYLOID FIBRILS TO THEIR ASSEMBLY MECHANISM AND CYTOTOXICITY... 

The self-assembly mechanism proposed for these spherical and cylindrical polymer backbones surrounded with quasi-equivalent dendritic coats is outlined in Figure 12.9. This knowledge allows the rational design of polymers with well defined spherical and cylindrical shapes. Quasi-equivalent character of these... 

Mechanical and Chemical Stability. The materials must maintain their mechanical properties and their chemical structure, composition, and surface over the course of time and temperature as much as possible. This characteristic relates to the essential reliability characteristic of energy on demand. Initially, commercial systems were derived from materials as they are found in nature. Today, synthetic materials can be produced with long life and excellent stability. When placed in a battery, the reactants or active masses and cell components must be stable over time in the operating environment. In this respect it should be noted that, typically, batteries reach the consumer 9 months after their original assembly. Mechanical and chemical stability limitations arise from reaction with the electrolyte, irreversible phase changes and corrosion, isolation of active materials, and local, poor conductivity of materials in the discharged state, etc. 

Also see Protein Polymerization Self-Assembly Mechanisms. 

Tang C, Smith AM, Colhns RE, UUjn RV, Saiani A (2009) Fmoc-diphenylalanine self-assembly mechanism induces apparent pK(a) shifts. Langmuir 25 9447-9453... 

For example, if fresh POPC from a methanol solution is added to a POPC hposome solution, there will be an immediate formation of fresh liposomes. In fact, the cmc in this case is of the order of 10 ° in favor of the aggregates over the free monomers, and the rate of formation is correspondingly extremely high. Thus, we are in the presence of an independent self-assembly mechanism. 

Another parameter which plays a role in the self-assembly mechanism is the pre-hydrolysis step present in preparation B. This procedure involved the addition of ethanol to the two precursors (EtOH/Si = 1 1) before reaction with the CTAB solution. We have thus investigated the role that ethanol could play in the organization of the final samples. 

Figure 7.13. Types of seals for pump shafts, (a) Packed stuffing box the sealing liquid may be from the pump discharge or from an independent source, (b) Water cooled stuffing box. (c) Internal assembly mechanical seal the rotating and fixed surfaces are held together by the pressure of the pump liquid which also serves as lubricant a slight leakage occurs, (d) Double mechanical seal with independent sealing liquid for handling toxic or inflammable liquids.

The information on protein structure is transmitted from the DNA in the cell nucleus to the cytoplasm where the protein is assembled by messenger RNA. This messenger RNA, or at least part of it, is assembled in the nucleus with a base sequence that is complementary to the base sequence in the parent DNA. The assembly mechanism is similar to DNA replication except that thymine (T) is replaced by uracil (U). The uracil is complementary to adenine in the DNA chain. (See Figure 25-27.) After the mRNA is assembled, it is transported to the cytoplasm where it becomes attached to the ribosomes. 

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