Tn''10'' is a

transposable element A transposable element (TE), also transposon, or jumping gene, is a type of mobile genetic element, a nucleic acid sequence in DNA that can change its position within a genome. The discovery of mobile genetic elements earned Barbara McClinto ...

, which is a sequence of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

that is capable of mediating its own movement from one position in the DNA of the host organism to another. There are a number of different transposition mechanisms in nature, but Tn''10'' uses the non-replicative cut-and-paste mechanism. The

transposase A transposase is any of a class of enzymes capable of binding to the end of a transposon and catalysing its movement to another part of a genome, typically by a cut-and-paste mechanism or a replicative mechanism, in a process known as transpositio ...

protein recognizes the ends of the element and cuts it from the original locus. The protein-DNA complex then diffuses away from the donor site until random collisions brings it in contact with a new target site, where it is integrated. To accomplish this reaction the 50 kDa transposase protein must break four DNA strands to free the transposon from the donor site, and perform two strand exchange reactions to integrate the element at the target site. This leaves two strands unjoined at the target site, but the host DNA repair proteins take care of this. The target site selection is essentially random, but there is a preference for the sequence 5'-GCTNAGC-3'. The 6-9 base pairs that flank the sequence also influence selection of the insertion site. Cut-and-paste transposition does not cause an increase in the number of transposons per se: there is one copy at the start and one copy at the end. If this was the end of the matter the transposon would perish by

genetic drift Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...

and the loss of copies owing to the occasional failure to achieve successful integration at the target site. However, the transposon has a mechanism to favor transposition immediately after a replication fork passes through, leaving a hemimethylated copy of Tn''10'' on each sister

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

. Since transposition is favored when Tn''10'' is hemimethylated, the transposon on one sister chromosome can hop somewhere onto the other chromosome so that two copies of the transposon end up on one chromosome. Tn''10'' has a composite structure and it is composed of a pair of insertion sequence elements (IS''10'') flanking five genes. Only one of the IS''10'' elements encodes a functional transposase. Since the ends of the IS''10'' element contain the transposase recognition sites, Tn''10'' has a total of four such sites. If the transposase binds the two recognition sites flanking an IS''10'' element, the IS''10'' element undergoes transposition independently of the larger composite structure. If the transposase binds the two outermost recognition sites, the whole composite Tn''10'' structure undergoes transposition. Two of the five genes encoded by the central portion of Tn''10'', ''tetA'' and ''

tetR Tet Repressor proteins (otherwise known as TetR) are proteins playing an important role in conferring antimicrobial resistance, antibiotic resistance to large categories of bacterial species. Tetracycline (Tc) is a broad family of antibiotics to w ...

'', confer resistance to the

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting pathogenic bacteria, bacterial infections, and antibiotic medications are widely used in the therapy ...

tetracycline Tetracycline, sold under various brand names, is an antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...

. This activity of tetR forms the basis of the TetOFF assembly, a widely used construct in synthetic gene studies. The TetA protein is an

efflux pump An efflux pump is an active transporter in cells that moves out unwanted material. Efflux pumps are an important component in bacteria, particularly in their ability to remove antibiotics. The efflux process can also involve the movement of hea ...

. It has served as a model system for such proteins and has accumulated hundreds of publications indexed in PubMed. The functions of the other three genes, ''jemA'', ''jemB'' and ''jemC'', are unknown but they may implicated in heavy metal resistance or

oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...

.Chalmers R, Sewitz S, Lipkow K, Crellin P (2000) Complete nucleotide sequence of Tn''10''" ''J Bacteriol'' 182: 2970-2972 The Tn''10''/IS''10'' transposase is closely related to another composite transposon, Tn''5''/IS''50'', which harbors a gene for

kanamycin Kanamycin A, often referred to simply as kanamycin, is an antibiotic used to treat severe bacterial infections and tuberculosis. It is not a first line treatment. It is used by mouth, injection into a vein, or injection into a muscle. Kanamy ...

resistance in the unique (i.e. non-repeated) central region of the transposon. The Tn''10'' transposon is often used in

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...

to transfer and select-for genes of interest from one organism into the chromosome of another. The mechanism of Tn''10'' transposition has served as a model system and the

archetype The concept of an archetype ( ) appears in areas relating to behavior, historical psychology, philosophy and literary analysis. An archetype can be any of the following: # a statement, pattern of behavior, prototype, "first" form, or a main mo ...

for the cut-and-paste mechanisms. However, the transposase is difficult to work with

in vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

and the Tn5 transposase was the first to be crystallized. Tn''10'' was one of the great work-horses of bacterial genetics for many years during which it served as a useful tool. A commercial kit for Tn''5'' transposition is commercially available and is extensively used in post-genomic technologies.

References

Further reading