transduction(redirected from Phototransduction)
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transduction,in genetics: see recombinationrecombination,
process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents.
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A mechanism for the transfer of genetic material between cells. The material is transferred by virus particles called bacteriophages (in the case of bacteria), or phages. The transfer method differentiates transduction from transformation. In transformation the genetic material (deoxyribonucleic acid) is extracted from the cell by chemical means or released by lysis. See Bacterial genetics, Bacteriophage, Deoxyribonucleic acid (DNA), Transformation (bacteria)
The transduction mechanism has two features to distinguish it from the more usual mechanism of gene recombination, the sexual process. The most striking feature is the transfer of genetic material from cell to cell by viruses. The second feature is the fact that only a small part of the total genetic material of any one bacterial cell is carried by any particular transducing particle. However, in general transduction, all of the genetic material is distributed among different particles.
Transduction is not accomplished by all bacteriophages. It is done by some that are classified as “temperate.” When such temperate bacteriophages infect sensitive bacteria, some of the bacteria respond by producing more bacteriophage particles. These bacteria donate the transducing material. Other bacteria respond to the infection by becoming more or less permanent carriers of the bacteriophage, in a kind of symbiotic relationship; these are called lysogenic bacteria. Bacteria in this latter class survive the infection, and it is among these that transduced cells are found. The proportion of bacteria in any culture that responds to infection in either manner can be influenced by the particular environment at the time of infection. See Lysogeny
Certain phages carry out a more restricted kind of transduction. They carry only a specific section of bacterial genetic material; they transduce only a few genes. Retroviruses carry out specific or restricted transduction. It has long been known that these viruses can cause the formation of tumors (oncogenesis) in animals. It is now known that these viruses exchange a small portion of their genome for a mutant cellular gene that has a role in gene regulation or replication. These viruses carrying mutant genes infect cells, causing them to be transformed into tumor cells. See Animal virus, Retrovirus
the transfer of genetic material from one cell to another by means of a virus; it leads to a change in the hereditary properties of the recipient cells. The phenomenon was discovered by the American geneticists J. Lederberg and N. Zinder in 1952.
In transduction, special bacterial viruses called mild phages are able during the process of vegetative reproduction to attach themselves at random to parts of DNA bacteria that they have lysed (disintegrated) and to transfer these parts to other cells. This process is called general, or nonspecific, transduction. The length of the transferred (transduced) fragment of DNA is determined by the size of the protein membrane of the phage particle, and usually does not exceed 1–2 percent of the bacterial genome. The transferred fragment may contain several genes.
Since the probability of linked transduction depends on the distance between genes in the particular DNA molecule that constitutes the bacterial chromosome, the transduction phenomenon is widely used to construct genetic maps of bacterial chromosomes. The genetic material of the phage is absent from the transduced particles; consequently, when the particles introduce DNA into the cell they do not perform all the other functions of phages: they do not reproduce, lysogenize the cell, or give it immunity to phages.
The introduced DNA fragment may exist in the cell in the-form of an additional genetic element that is capable of functional activity. Since this fragment is not capable of reproduction, it is transferred to only one of the daughter cells with each cell division. Except for this cell, the properties of the remaining offspring remain unchanged (abortive transduction). Subsequently, the fragment may either disintegrate or become part of the bacterial chromosome, replacing the homologous part of DNA in the chromosome. If this occurs, the new characteristics acquired by the recipient cell will be inherited by all offspring of that cell (complete transduction).
A different type of phage is capable of transducing only certain genes that are located next to the site where the phage genome is included in the bacterial chromosome during lysogenization (limited, or specific, transduction). Such transduced phage particles, formed owing to accidental disruption of the normal emergence of prophage from the bacterial chromosome, contain a DNA molecule that consists of a remnant of a phage genome and a fragment of a bacterial genome. In most cases, these phage particles cannot reproduce independently or lysogenize bacteria owing to a loss of parts of the phage genome amounting to as much as 30 percent. The genetic material of the transducing particles may be retained in the cell in an autonomous state or be included in the bacterial DNA as prophage. In both cases some of the offspring reestablish the original properties, owing to the loss of prophage. Stable transduction occurs only when the bacterial fragment of prophage is included in the bacterial genome as a result of an exchange on the homologous part of the chromosome.
REFERENCESStent, G. Molekuliarnaia biologiia virusov bakterii. Moscow, 1965. (Translated from English.)
Stent, G. Molekuliarnaia genetika. Moscow, 1974. Chapter 14. (Translated from English.)
A. N. MAISURIAN