Insertion sequence

Type of transposable element in bacteria

Insertion sequence

An insertion sequence (IS) is a simple type of transposable element found in prokaryotes, such as bacteria and archaea. These genetic elements are capable of moving from one location to another within the genome, a process known as transposition. Insertion sequences are the simplest form of transposable elements and are typically composed of a single gene that encodes a transposase enzyme, flanked by inverted repeats.

Structure

Composite transposon structure

Insertion sequences are characterized by their simple structure. They usually consist of:

• A single gene that encodes the transposase enzyme, which is responsible for catalyzing the movement of the IS element.
• Inverted repeat sequences at both ends of the element, which are recognized by the transposase during the transposition process.

The length of an insertion sequence can vary, typically ranging from 700 to 2500 base pairs. The inverted repeats are usually 10 to 40 base pairs long.

Function

The primary function of insertion sequences is to facilitate their own movement within the genome. The transposase enzyme recognizes the inverted repeats and catalyzes the excision of the IS element from its original location. The element is then inserted into a new site within the genome. This process can result in mutations if the insertion disrupts a functional gene or regulatory region.

Insertion sequences can also play a role in genetic recombination and horizontal gene transfer, contributing to genetic diversity and evolution in bacterial populations. They can influence the expression of nearby genes and can be involved in the formation of more complex transposable elements, such as composite transposons.

Impact on Host Genome

Insertion sequences can have various effects on the host genome, including:

• Mutagenesis: Insertion into a gene can disrupt its function, leading to loss of function mutations.
• Gene regulation: Insertion sequences can affect the expression of nearby genes, either by providing new promoters or by disrupting existing regulatory sequences.
• Genome rearrangements: Multiple insertion sequences can facilitate recombination events, leading to deletions, inversions, or duplications of genomic regions.

Applications

Insertion sequences are used as tools in molecular biology and genetic engineering. They can be employed to create mutant strains of bacteria for research purposes, to study gene function, and to investigate the mechanisms of transposition.

Related pages

• Transposon
• Transposase
• Horizontal gene transfer
• Genetic recombination