Transposons


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Transposons

Types of transposable elements which comprise large discrete segments of deoxyribonucleic acid (DNA) capable of moving from one chromosome site to a new location. In bacteria, the transposable elements can be grouped into two classes, the insertion sequences and the transposons. The ability of transposable elements to insert into plasmid or bacterial virus (bacteriophage) which is transmissible from one organism to another allows for their rapid spread. See Bacteriophage, Plasmid

The insertion sequences were first identified by their ability to induce unusual mutations in the structural gene for a protein involved in sugar metabolism. These insertion sequences are relatively small (about 500–1500 nucleotide pairs) and can only be followed by their ability to induce these mutations. Most bacterial chromosomes contain several copies of such insertion sequence elements.

The transposons are larger segments of DNA (2000–10,000 base pairs) that encode several proteins, usually one or two required for the movement of the element and often an additional protein that imparts a selective advantage to the host containing a copy of that element. The structure of many transposons suggests they may have evolved from the simpler insertion sequence elements.

All transposable elements, both the simple insertion sequence elements and the more complex transposons, have a similar structure and genetic organization. The ends of the element represent recognition sites and define the segment of DNA undergoing transposition. A short sequence present at one end of the element is repeated in an inverted fashion at the other end. These terminal inverted repeats are characteristic for each element.

Members of a widespread group of transposons, the Tn3 family, all have a similar structure and appear to move by a similar mechanism. Transposase, one protein encoded by the element, promotes the formation of intermediates called cointegrates, in which the element has been duplicated by replication. A second element-encoded protein, resolvase, completes the process by converting the cointegrates into the end products of transposition, a transposon inserted into a new site. A third protein encoded by the Tn3 element imparts resistance to the antibiotic ampicillin.

Transposons are known that encode resistances to almost all antibiotics as well as many toxic metals and chemicals. In addition, some transposons have acquired the ability to direct the synthesis of proteins that metabolize carbohydrates, petroleum, and pesticides. Other transposable elements produce enterotoxins that cause travelers to become ill from drinking water contaminated with bacteria carrying the element. The broad spectrum of activities encoded by the transposable elements demonstrates the strong selective advantage that has accompanied their evolution.

Transposable elements are not restricted to prokaryotes. Yeast as well as higher eukaryotes have DNA segments that move and cause mutations. The eukaryotic elements have much in common with their prokaryotic counterparts: the termini of the elements are composed of inverted repeats, and many of the larger elements are composed of two small insertion sequence-like regions flanking a unique central region. One class of eukaryotic virus, the ribonucleic acid (RNA) retrovirus, also has this structure and is thought to integrate into the host chromosome through a transpositionlike mechanism. See Antibiotic, Gene, Gene action, Retrovirus, Virus

References in periodicals archive ?
The Spread of Klebsiella pneumoniae Carbapenemases: A Tale of Strains, Plasmids, and Transposons.
We found that retrovirus-related Pol polyproteins from transposons were strongly differentially expressed starting at 90 min (Fig.
P{MiET1} mutants, which are homozygous lines with Minos transposon insertions in a common genetic background (Bellen et al.
Based on the sequence variation information caused by transposon insertions, 6 pairs of STS primers were designed to detect 10 allelic variation types of the waxy gene in eleven foxtail millet strains.
Transposons were discovered in the 1940s by Barbara McClintock, who was rewarded in 1983 with the Nobel Prize for Physiology or Medicine.
The association of markers with known genes as well as with transposon elements was also investigated.
Analysis by transposon display of the behavior of the dTphl element family during ontogeny and inbreeding of Petunia hybrida.
plasmids and transposons are mainly responsible for the spread of resistance in the hospitals as well as in the community ecosystem.
Certain DNA elements such as transposons, fragments of DNA that replicate within an organism's genome, can however disrupt this functioning and disable genes.
The insertion locations of these moveable segments EoACAo transposons EoACAo in each individualEoACAOs genome helps determine why some are short or tall, blond or brunette, and more likely or less likely to have cancer or heart disease.
The nine studies cover catalytic activity in transcripts from Schistosoma non-autonomous retro-transposons, mobile genetic elements of malaria vectors and other mosquitoes, retro-transposons in the genomes of the digenean parasitic trematodes Clonochis sinensis and Paragonimus westermani, endogenous retro-transposon sequences of the Schistosoma mansoni intermediate snail host Biomphalaria glabrata, the transposon-mediated transgenis of mosquitoes, Schistosome long terminal repeat retro-transposons colonizing Schistosome genomes, Schistosome DNA transposons, and mobile genetic elements resident in hookworm genomes.