A transposon is a mobile genetic element that can move from one position in a genome to another, altering the genomic landscape.
Mechanisms and Importance
Transposons, often called jumping genes, were discovered by Barbara McClintock during her studies of maize and are now recognised in all domains of life. They fall into two major classes. Class I transposons, or retrotransposons, transpose via an RNA intermediate: the element is transcribed into RNA, reverse‑transcribed into DNA and integrated at a new site, resulting in a copy‑and‑paste mechanism that increases copy number. This class includes long terminal repeat retrotransposons related to retroviruses and non‑LTR elements such as long and short interspersed nuclear elements. Class II transposons are DNA elements that move directly as DNA. Many use a cut‑and‑paste mechanism in which a transposase enzyme excises the element at the termini and inserts it elsewhere; others replicate during transposition. Structural hallmarks include terminal inverted repeats and a gene encoding a transposase. Movement of transposons can disrupt genes, alter regulation and promote genome rearrangements, making them important drivers of evolution. Composite transposons in bacteria often carry antibiotic resistance or metabolic genes and can transfer between plasmids and chromosomes, facilitating horizontal gene transfer. In laboratories, transposon mutagenesis is used to identify gene functions, and synthetic transposon systems are being developed for gene therapy applications.
Key Examples and Impacts
The Ac/Ds system in maize is a classic DNA transposon pair responsible for mottled kernel patterns, illustrating cut‑and‑paste transposition. P elements in Drosophila melanogaster are widely used to insert reporter constructs and create mutant lines. Bacterial transposon Tn5 carries a kanamycin resistance gene and serves as a tool for mutagenesis in Gram‑negative bacteria; Tn10 confers tetracycline resistance. In humans, Alu and LINE‑1 retrotransposons comprise a large proportion of the genome and contribute to insertion polymorphisms and genomic variation. The Sleeping Beauty transposon, reconstructed from a salmonid fish, is engineered for efficient gene insertion in vertebrate cells and is being explored for gene therapy. These examples underscore the diverse roles of transposons in natural biology and biotechnology.
Transposons are ubiquitous genetic elements that shape genome structure and function. Their mobility drives diversity but can also cause disease when insertions disrupt essential genes. Harnessing transposon biology has provided powerful tools for genetics, biotechnology and medicine.
Related Terms: transposase, insertion sequence, retrotransposon, genome plasticity, mutation