8 Viral Translational Strategies and Host Defense Mechanisms

Abstract

Viruses are obligate intracellular parasites or symbionts and depend on cells for their replication. Virus–cell interactions reflect this dependency as well as the efforts of the host to combat infection, and of the virus to counter host defenses. Because of the intimate nature of these relationships between the protagonists, the study of viruses continues to shed light on the detailed workings of host systems at a variety of levels.

Viruses lack the enzymes and associated apparatus for conducting most metabolic and biosynthetic reactions. Instead, they rely on the cells that they infect to supply energy, chemicals, and most of the necessary biosynthetic machinery. Many viruses encode enzymes for nucleic acid biosynthesis, but—with the rare exceptions described below—they do not encode any part of the translational apparatus. They are therefore forced to make use of the cellular apparatus for the synthesis of one of their principal components. As a consequence, and because they can be manipulated with some ease, viral systems have historically provided penetrating insights into the workings of the protein synthetic machinery. Some landmark discoveries made with viruses are listed in Table 1.

In their interactions with the host translation system, viruses do more than simply co-opt the cellular machinery, however. They have adopted regulatory mechanisms from their hosts and perhaps invented some of their own, although several seemingly unorthodox viral mechanisms are now recognized in the cells’ own repertoire. Nevertheless, it is difficult to avoid the impression that a greater range and diversity of tactics...