Transposons are mobile genetic elements that are found in almost all organisms. Scientists believe that transposons make up more than 40% of the human genome. They are also referred to as ‘jumping genes’ as they can move (or jump) from one location in the genome to another.
There are two distinct types of transposons based on requirements of reverse transcription in order to transpose or not.
- Retrotransposons: First transcribe the DNA into RNA and then use reverse transcriptase to make a DNA copy of the RNA to insert in a new location (i.e. requires reverse transcription). They are also known as class 1 transposable elements (TEs).
- DNA transposons: Transposons consisting only of DNA that moves directly from place to place (cut and paste mechanism). They are also called class 2 transposable elements (TEs).
Features of Bacterial Transposons
- Transposons are pieces of DNA that move readily from one site to another, either within or between the DNA’s of bacteria, plasmids, and bacteriophage.
- They can code for drug resistance enzymes, toxins, or a variety of metabolic enzymes.
They either cause mutations in the gene into which they insert or alter the expression of nearby genes.
- Transposons are not capable of independent replication; they replicate as part of the recipient DNA. eg. a plasmid can contain several transposons carrying drug resistance genes.
Transposable elements, or “jumping genes”, were first identified by Barbara McClintock in 1940s. She was awarded the Nobel Prize in Physiology or Medicine for 1983 for the discovery of “mobile genetic elements”.
Insertion sequences are a type of transposons that have fewer bases.
Domains of Transposons
Transposons have four identifiable domains.
- Inverted repeats (IR): Involved in the integration of the transposons into the recipient DNA.
- Transposase gene: It codes the enzyme that mediates the excision and integration process.
- Repressor gene: It regulates the synthesis of both the transposase and gene product of the fourth domain
- Fourth domain codes for an enzyme that mediates antibiotic resistance.