life11e_ch16

Eukaryotic viruses can have complex life cycles

Eukaryotes are susceptible to infection by various kinds of viruses whose genomes may consist of RNA or DNA. A subgroup of RNA viruses are called retroviruses.

DNA viruses. Many viral particles contain double-stranded DNA. However, some contain single-stranded DNA, and a complementary strand is made after the viral genome enters the host cell. Like some bacteriophages, DNA viruses that infect eukaryotes are capable of undergoing both lytic and lysogenic life cycles. Examples include the herpes viruses and papillomaviruses (which cause warts).
RNA viruses. Some viral genomes are made up of RNA that is usually, but not always, single-stranded. The RNA is translated by the host’s machinery to produce viral proteins, some of which are involved in replication of the RNA genome. The influenza virus has an RNA genome.
Retroviruses. As we described in Key Concept 14.2, a retrovirus is an RNA virus that carries a gene for reverse transcriptase, a protein that synthesizes DNA from an RNA template. The *retrovirus uses this protein to make a DNA copy of its genome, which then becomes integrated into the host genome. The integrated DNA acts as a template for both mRNA and new viral genomes. HIV is a retrovirus that infects cells of the immune system and causes acquired immune deficiency syndrome (AIDS).

*connect the concepts Viral diversity is discussed in Key Concept 25.4, which explains why the genomes of some viruses consist of single-stranded RNA and how RNA retroviruses reproduce themselves by reverse transcription.