Temperate bacteriophage

Viruses are discussed more fully elsewhere (Chapter 3). However, there are certain groups of viruses, called bacteriophages (phages), which can attack bacteria. This attack involves the injechon of viral DNA into baeterial eells which then proceed to make new virus particles and destroy eells. Some viruses, known as temperate viruses, do not cause this catastrophic event when they infect their host, but can pass genetic material from one cell to another. 

Figure 5.21 Consequences of infection by a temperate bacteriophage. The alternatives upon infection are integration of the virus DNA into the host DNA (lysogenization) or replication and release of mature virus (lysis). The lysogenic cell can also be induced to produce mature virus and lyse.

Viruses may also cause latent infection of a host. In a latent infection, there is a delay between infection by the virus and the appearance of symptoms. Fever blisters (cold sores), caused by the herpes simplex virus, result from a latent viral infection the symptoms reappear sporadically as the virus emerges from latency. The latent stage in viral infection of an animal cell is generally not due to the integration of the viral genome into the genome of the animal cell, as is the case with latent infections by temperate bacteriophages. 

Temperate bacteriophage, the best known being phage X, have a very different life cycle. Their DNA usually becomes integrated at a specific point into the genome of the bacterium (Chapter 27). Only rarely is an infected cell lysed. The retroviruses that attack mammals and birds have a similar characteristic. 

The temperate bacteriophage Mu. The most efficient transposon known is the 37-kb genome of the mutator bacteriophage Once it... 

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