Virus Assembly and Its Genetic Control

  • William B. Wood
Part of the Life Science Monographs book series (LSMO)


The genetic specification of virus parts is relatively well understood, but mechanisms of assembly to form complete viruses remain somewhat obscure. A simple virus like the tobacco mosaic virus can form by the process of self-assembly, in which all participating proteins are included in the final structure. Such viruses can spontaneously reassemble following dissociation of their parts. T4, a more complex virus, cannot do so. T4 has three major body parts: tail fibers, a tail, and a head composed of a DNA-containing capsid (head). These parts are assembled independently. Several T4 genes code for nonstructural proteins that are essential to the assembly of one of these parts but are not present in the finished virus. This dependency represents a clear departure from simple self-assembly. At least two features of T4 assembly cannot be explained in terms of thermodynamic equilibria alone: many assembly steps can occur in only one particular order, and only one capsid structure generally forms despite the possibility of alternative structures with roughly equal thermodynamic stability. Both features can be explained by rate controls on assembly steps. In T4, different kinds of protein subunits may affect each other’s association by means of induced conformational changes, so that each assembly step increases the rate of the next step. This hypothetical process is called heterocooperativity. (It has features reminiscent of the kinetics discussed by Schuster and Sigmund in Chapter 5.) Maintenance of protein ratios may confer another kind of kinetic control on capsid formation. At least three kinds of nonstructural accessory proteins are found in T4: scaffolding proteins, proteolytic enzymes, and promoters of noncovalent bonding. Self-assembly, kinetic controls, and accessory protein functions provide significant insight into the mechanism of self-organization in viruses. (The glossary in Chapter 5 may be helpful for this chapter also.) —The Editor


Tobacco Mosaic Virus Accessory Protein Phage Particle Assembly Step Tail Fiber 
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Copyright information

© Plenum Press, New York 1987

Authors and Affiliations

  • William B. Wood
    • 1
  1. 1.Department of Molecular, Cellular, and Developmental BiologyUniversity of ColoradoBoulderUSA

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