Oo

^N. Mouse dies

Living encapsulated cells isolated

Heat-killed encapsulated cells oo.

Non-encapsulated cells oo

Figure 1 Demonstration of the Transforming Principle

scientists were slow to recognize its significance and importance. None of the three investigators received a Nobel Prize, although many scientists believe that they deserved it.Their studies pointed out that DNA is a key molecule in the scheme of life and led to James Watson and

Francis Crick's determination of its structure, which they published in 1953.The understanding of the structure and function of DNA revolutionized the study of biology and ushered in the era of molecular biology. Microbial genetics serves as the foundation of molecular biology.

Francis Crick's determination of its structure, which they published in 1953.The understanding of the structure and function of DNA revolutionized the study of biology and ushered in the era of molecular biology. Microbial genetics serves as the foundation of molecular biology.

8.8 Transduction

Bacterial viruses, called bacteriophage or simply phage, will also transfer bacterial genes from one cell to another by a process called transduction. Phage have a protein coat that surrounds the genetic material of the virus. The phage infect bacteria, multiply inside the cells, and then are released by lysing the cells. Some of the released phage may carry bacterial genes in place of phage genes inside their protein coats. The phage containing bacterial genes then infect other bacteria and can transfer bacterial genes from the first infected bacterium to the second (figure 8.16). There are two types of transduction: generalized and specialized. In generalized transduction, any gene of the donor cell can be transferred. In specialized transduction, only a few specific genes can be transferred. We will briefly cover generalized transduction now and both will be discussed in more detail when the replication cycles of bacteriophage are considered in chapter 13.

In generalized transduction, after the phage infects the bacterium, the phage encoded enzyme deoxyribonuclease is expressed. This enzyme cleaves the replicated phage DNA into the proper size fragments to be enclosed in the coat protein of the phage. However, this deoxyribonuclease also cleaves the bacterial chromosome into fragments, which also can become surrounded by the phage coat, taking the place of phage DNA. Once released from the infected cell, the phage containing the bacterial DNA may infect other nearby cells and thereby transfer bacterial genes. Inside the recipient cell, the bacterial DNA becomes integrated by homologous recombination, replacing genes in the recipient cell. Transduction is a common mechanism of gene transfer and occurs in a wide variety of Gram-positive and Gram-negative bacteria.

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