Virus capsid synthesis

The late phase of the infectious cycle involves the synthesis of structural proteins of the virus, capsid assembly, genome encapsidation, and maturation of fully infectious viral particles. These events are associated with the transcription and translation of the late genes LI to L5 [26, 27]. A key player in the transcription of the late genes is the major late promoter (MLP), which is activated early on via the E2 gene [27, 29],... 

Several approaches have recently been developed that directly apply natural architectures for artificial chanical reactions, some of which are detailed in different chapters of this book. Although not classified as homogeneous catalysis, the reduction of metal salts inside nanoreactors could be the first step on the way to reactivity with the corresponding metal coUoids or nanoparticles in e.g. hydrogenation reactions. A variety of carrier systems have been studied lately, including virus capsids, polymeric micelles, miniemulsions and hollow core-shell particles, as nanoreactors and hosts for the synthesis and encapsnlation of well-defined, stable nanoparticles. ... 

One particular asset of structured self-assemblies is their ability to create nano- to microsized domains, snch as cavities, that could be exploited for chemical synthesis and catalysis. Many kinds of organized self-assemblies have been proved to act as efficient nanoreactors, and several chapters of this book discnss some of them such as small discrete supramolecular vessels (Chapter Reactivity In Nanoscale Vessels, Supramolecular Reactivity), dendrimers (Chapter Supramolecular Dendrlmer Chemistry, Soft Matter), or protein cages and virus capsids (Chapter Viruses as Self-Assembled Templates, Self-Processes). In this chapter, we focus on larger and softer self-assembled structures such as micelles, vesicles, liquid crystals (LCs), or gels, which are made of surfactants, block copolymers, or amphiphilic peptides. In addition, only the systems that present a high kinetic lability (i.e., dynamic) of their aggregated building blocks are considered more static objects such as most of polymersomes and molecularly imprinted polymers are discussed elsewhere (Chapters Assembly of Block Copolymers and Molecularly Imprinted Polymers, Soft Matter, respectively). Finally, for each of these dynamic systems, we describe their functional properties with respect to their potential for the promotion and catalysis of molecular and biomolecu-lar transformations, polymerization, self-replication, metal colloid formation, and mineralization processes. 

The first step in the replication of influenza viruses, which takes place in the cytoplasm, is the synthesis of (+) strands that can serve both as mRNA for synthesis of proteins and as templates for synthesis of new (-) strands. Three of the capsid proteins form the required RNA polymerase. This "transcriptase" is primed preferentially by 5 -capped 10- to 13-nucleotide segments of RNA that have been cut by a viral nuclease from host mRNAs.700 The mRNAs made from viral RNA are polyadenylated and are translated by the host cell s ribosomes. However, some transcripts are used as templates to form viral (-) strands, which... 

Trempe, J. P. and Carter, B. J. (1988). Alternate mRNA splicing is required for synthesis of adeno-associated virus VP1 capsid protein. J. Virol. 62, 3356-3363. 

Synthesis of viral capsid protein, envelope protein, reverse transcriptase. Assembly of new virus and release by budding... 

An excellent example where a capsid virus has been given a new supramolecular application can be found in the work of Nolte who took an icosahedral capsid virus, cowpea chloritic mottle virus (CCMV) and used it as a nanoreactor for polymer synthesis [30], Natural CCMV spontaneously assembles in acidic aqueous solution and disassembles in basic solution. The capsid contains pores open at pH 5 to release RNA into the host. Once the RNA leaves, the empty capsule is left. The Nolte group was able to assemble the subunits around polystyrene sulfonate with a mass of 9.9 kDa but the resulting structure had a different morphology to the natural system. Indeed, capsules formed around polymers with masses between 2 and 85 kDa but not around those with masses above 100 kDa. This raised the question of the potential for polymers to form within a capsid but to test the possibility a mixture of botanical, biological and chemical approaches was needed. 

Another general role of post-translational cleavage of polypeptide chains in viral systems is the specific processing of structural proteins leading to the assembly of the virus (44,45). In this respect, the semliki-Forest virus may be considered as an interesting model to find out how proteins which have different cellular locations reach their final sites within the cell. A single messenger RNA directs the synthesis of the viral capsid protein and of two membrane proteins. 

As a close relative to the brome mosaic virus the cowpea chlorotic mottle vims (CCMV) possesses an outer diameter of 28 nm, is assembled from 180 subunits that create an icosahedral type structure, and contains an RNA core. " Another similarity is the cationic interior surface of the viral capsid which is formed from subunits with highly basic N-termini (6 positively charged arginine and 3 lysine residues) that project into the cavity and stabilize the RNA core. However as a potential biomineralization template, the electrostatic environment of the virion cavity precludes any cationic metal precursors and thus limits its applicability for nanoparticle synthesis. 

Grimes et al., 1998 Reinisch et al, 2000 Wikoff et at, 2000). Likewise, advances in electron cryomicroscopy and image reconstruction techniques allow time-resolved investigations of structural transitions associated with capsid assembly and maturation (Conway et al., 2001 Lawton et al, 1997). These developments have been paralleled by refinements in the molecular approaches used for sample preparation, with the result that synthesis of assembly intermediates and end products has become routine for many viruses. 

Viral DNA synthesis Viral capsidation Virus absorption Protein kinase C Virucidal, late proteins synthesis Unknown... 

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