Transposase

Transposase

Structure of a transposase enzyme.

Another view of the transposase structure.

Transposase is an enzyme that catalyzes the movement of transposons, or "jumping genes," within the genome. This process is known as transposition. Transposases are essential for the genetic recombination that allows transposons to move from one location to another within the DNA of a cell.

Function

Transposases recognize specific DNA sequences at the ends of the transposon and facilitate the cutting and rejoining of DNA strands. This allows the transposon to be excised from its original location and inserted into a new site within the genome. The enzyme typically makes a staggered cut in the target DNA, which is then repaired by the cell's DNA repair machinery, resulting in the integration of the transposon.

Mechanism

The mechanism of transposition involves several steps:

1. Binding: The transposase binds to the ends of the transposon at specific sequences known as terminal inverted repeats (TIRs). 2. Cleavage: The enzyme cleaves the DNA at the ends of the transposon, releasing it from its original site. 3. Integration: The transposase inserts the transposon into a new target site in the genome.

This process can be either "cut and paste," where the transposon is excised and reinserted, or "copy and paste," where a copy of the transposon is inserted into a new location while the original remains in place.

Types of Transposases

Transposases can be classified into several families based on their structure and mechanism of action. Some of the well-known families include:

• DDE transposases: Characterized by a conserved DDE motif, these are the most common type of transposases.
• Tyrosine transposases: These use a tyrosine residue to mediate the transposition reaction.
• Serine transposases: These use a serine residue in their active site.

Biological Significance

Transposases play a crucial role in genetic diversity and evolution. By facilitating the movement of transposons, they contribute to genome plasticity, allowing organisms to adapt to changing environments. However, uncontrolled transposition can lead to genomic instability and is associated with various genetic disorders and cancers.

Related Pages

• Transposon
• Genetic recombination
• DNA repair

References

• Craig, N. L., et al. (2002). "Mobile DNA II." ASM Press.
• Chandler, M., et al. (2015). "Transposition, Recombination and DNA Repair." Springer.