X174

Productive

ss DNA

Cell lyses

*ds, double-stranded; ss, single-stranded.

334 Chapter 13 Viruses of Bacteria

The DNA of a temperate phage enters into the bacterial host cell.

The phage DNA may become integrated with host cell DNA as a prophage.

The phage DNA may become integrated with host cell DNA as a prophage.

The phages that are replicated are defective because they lack some viral genes that have been replaced by bacterial DNA. Note that the phage heads contain both phage and bacterial DNA.

The defective phage DNA enters new host cells but cannot cause the production of new phage particles.

Bacterial genes introduced into the new host cell are integrated into the DNA, become a part of the bacterial chromosome, and are replicated along with the rest of the bacterial DNA.

The phages that are replicated are defective because they lack some viral genes that have been replaced by bacterial DNA. Note that the phage heads contain both phage and bacterial DNA.

The defective phage DNA enters new host cells but cannot cause the production of new phage particles.

Bacterial genes introduced into the new host cell are integrated into the DNA, become a part of the bacterial chromosome, and are replicated along with the rest of the bacterial DNA.

Figure 13.11 Specialized Transduction by Temperate Phage

Only bacterial genes near the site where the prophage has integrated can be transduced.

Usually, only the phage l DNA is excised following induction. On rare occasions, however, a piece of bacterial DNA remains attached to the piece of phage DNA that is excised and a piece of phage DNA is left behind in the bacterial chromosome. This loss of phage DNA creates a defective phage. The bacterial genes attached to the phage DNA replicate as the phage DNA replicates. This DNA molecule consisting mostly of bacterial DNA but also containing some phage genes, then becomes incorporated into mature phage in the maturation process. The defective phage is released from the lysed cells. When the defective phage infects another bacterial cell, both phage and bacterial DNA enters the new host and becomes integrated into the chromosome. Thus, the resulting lysogen contains bacterial genes from the previously lysogenized cell. Only bacterial genes located near the site of integration of the phage DNA can be transduced.

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