Transposase
Enzymes that move DNA segments within genomes.
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A transposase is an enzyme that binds to the ends of a transposon and catalyzes its movement to another location in a genome, typically through cut-and-paste or replicative mechanisms. The term was coined by the researchers who cloned the enzyme required for transposition of the Tn3 transposon. Transposases are classified under EC number 2.7.7 and are among the most abundant genes known, with transposition events contributing to genetic diversity and, in humans, to the movement of up to 40% of the genome.
Quick Facts
- Classification
- Enzyme class
- Function
- Catalyzes transposition of transposons
- Known for
- Most abundant genes in genomes; involved in genetic diversity and antibiotic resistance
Facts from the source article.
Transposase Tn5
Transposase Tn5 is a member of the RNase superfamily of proteins, which also includes retroviral integrases, and is found in Shewanella and Escherichia bacteria. The Tn5 transposon codes for resistance to kanamycin and other aminoglycoside antibiotics. Tn5 and many other transposases are notably inactive, as DNA transposition events are inherently mutagenic; low activity reduces the risk of causing a fatal mutation in the host. One reason for Tn5's low reactivity is that its N- and C-termini are located close together and tend to inhibit each other.
This was clarified by characterizing mutations that produce hyperactive forms; for example, the L372P mutation replaces leucine with proline at amino acid 372, breaking an alpha helix and causing a conformational change that separates the C-terminal domain from the N-terminal domain, promoting higher activity. Tn5 uses a cut-and-paste mechanism and requires only the transposon, the transposase enzyme, and target DNA for insertion. Most Tn5 and other transposases contain a DDE motif—aspartate-97, aspartate-188, and glutamate-326—that forms the active site and coordinates divalent metal ions such as magnesium and manganese. Because the wild-type transposase is highly inactive, the DDE region is mutated to create hyperactive forms for study, though some catalytic steps are lost.
Sleeping Beauty transposase
The Sleeping Beauty transposase is the enzyme that controls the SB transposon system. It is a member of the DD[E/D] family of transposases, which are part of a broader superfamily of polynucleotidyl transferases.
This group also includes RNase H, RuvC Holliday resolvase, RAG proteins, and retroviral integrases. In vertebrate animals, the SB system is mainly applied to gene transfer, including gene therapy and gene discovery. The modified version SB100X achieves high rates of transposon integration.
Tn7 transposon
The Tn7 transposon is a mobile genetic element found in many prokaryotes such as Escherichia coli, first discovered as a DNA sequence in bacterial chromosomes and plasmids that encoded resistance to trimethoprim and streptomycin. It duplicates and moves itself within a genome using a self-encoded transposase, which can create or reverse mutations and change genome size. Tn7 has two mechanisms for propagation: low-frequency transposition into many sites with little selectivity, preferentially into conjugable plasmids that can spread between bacteria; and high-frequency transposition into a single specific site in bacterial chromosomes called attTn7. This site is an essential, highly conserved gene, but Tn7 inserts downstream of it without harming the host, promoting coexistence and transmission.
The Tn7 transposon is 14 kb long and codes for five enzymes. Its ends consist of a left segment (Tn7-L, 150 bp) and a right segment (Tn7-R, 90 bp), each containing 22 bp binding sites recognized by the transposase. Within the transposon are five genes encoding the transposition machinery and an integron containing cassettes of antibiotic-resistance genes.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Transposase (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
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