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The retrovirus family encompasses a diverse group of metazoan viruses that have a replication step whereby DNA is synthesized from virion RNA in a process designated reverse transcription (Temin and Baltimore, 1972) (Fig. 1; Table I) (see Chapter 1). Molecular mechanisms in the virus life cycle are reviewed in this chapter, and the focus is on retroviruses containing genes for virion proteins but lacking genes that regulate viral expression. Retroviruses with simple genomes express the polyproteins (i.e., precursor polypeptides) encoded by the following genes: gag for group-specific antigen in the virion core, pol for RNA-dependent DNA polymerase, and env for the viral envelope glycoproig. 2). This genome organization is a feature of three genera in the retrovirus family, and both horizontally transmitted exogenous viruses and vertically transmitted endogenous viruses are included (Table II) (see Chapters 1 and 2) (Coffin, 1982b; Coffin and Stoye, 1985). Retroviruses with complex genomes (i.e., lentiviruses, spumaviruses, and certain oncoviruses) encode regulatory genes as well as virion proteins; replication of these viruses is discussed in other chapters and volumes in this series (see also Green and Chen, 1990; Mergia and Luciw, 1991; Cullen, 1991; Haseltine, 1991). Nonetheless, many aspects of the life cycle of retroviruses with simple genomes are shared by all retroviruses. |
