18 Interactions between Viruses and the Cellular Machinery for Protein Synthesis

Abstract

Viruses are obligate intracellular parasites or symbionts. They are incapable of independent existence because they lack the enzymes and associated apparatus for conducting most metabolic and biosynthetic reactions. Instead, they rely on the cells that they infect to supply the energy, chemicals, and machinery required for virus replication. Nowhere is this dependence more apparent than in protein synthesis. Many viruses encode enzymes for nucleic acid biosynthesis, but – with the exception of some tRNAs – none of them is known to encode any part of the translational apparatus. They are therefore obligated to make use of the cellular translational apparatus for the synthesis of one of their chief components. As a consequence, and because they can be manipulated with some ease, viral systems have provided many insights into the workings of the cellular protein synthetic machinery. For example, analysis of mutations in the coat protein of tobacco mosaic virus and the rII cistron of bacteriophage T4 contributed to breaking the genetic code (Barnett et al. 1967; Wittmann and Wittmann-Liebold 1967), and biochemical evidence for the existence of messenger RNA (mRNA) came first from phage-infected bacteria (Volkin and Astrachan 1956; Brenner et al. 1961; Gros et al. 1961). Viral RNA was the natural template of choice for studies of messenger-directed protein synthesis in both prokaryotes and eukaryotes, leading to the development of faithfully initiating cell-free translation systems and thence to the identification of the initiator tRNAs and characterization of ribosome-binding sites (Nathans et al. 1962; Adams and Capecchi 1966; Kerr et al. 1966;...