Transposon

Transposons, or transposable elements, are DNA sequences that can move from one genomic location to another. They can disrupt genes, alter regulatory regions, create chromosomal rearrangements, and contribute to genome evolution by duplicating or rearranging genetic material. Their movement is typically regulated by the host genome and can be suppressed by epigenetic mechanisms.

There are two major classes based on their transposition mechanism. DNA transposons move by a cut-and-paste process: a transposase enzyme excises the element and inserts it elsewhere, often leaving behind short target site duplications. Retrotransposons move by a copy-and-paste process through an RNA intermediate: the element is transcribed, reverse-transcribed into DNA, and then integrated at a new site. Retrotransposons are subdivided into long terminal repeat (LTR) elements and non-LTR elements such as LINEs (long interspersed nuclear elements) and SINEs (short interspersed nuclear elements). Some transposons are autonomous, encoding the enzymes needed for mobility; others are non-autonomous and depend on enzymes from other elements.

Transposons are widespread in both prokaryotic and eukaryotic genomes and have a significant impact on genome size and structure. In genomes, they can drive evolution by creating new genes or regulatory networks and by promoting recombination. They also pose risks, including insertional mutagenesis and genome instability, leading to diseases in some contexts. Organisms deploy silencing strategies such as DNA methylation, small RNA pathways, and chromatin modifications to limit transposon activity.

Transposons were discovered in the 1940s by Barbara McClintock in maize, and later found to be a common feature across life. They are valuable tools in genetics and biotechnology for mutagenesis, tagging, and gene delivery.