ISEs

Insertion sequence elements (ISEs) are the simplest transposable elements found in bacteria and some archaea. They are short DNA sequences that can move within a genome, typically ranging from about 700 to 2,500 base pairs. ISEs usually encode a single enzyme called transposase, which catalyzes their movement, and they are flanked by terminal inverted repeats. When they insert into new sites, they often create short target-site duplications in the host DNA.

Mechanism and structure is focused on the transposase and the ends of the element. Transposase recognizes the inverted repeats at the element’s ends and mediates transposition. Movement can occur by non-replicative (cut-and-paste) transposition or, in some families, by replicative (copy-and-paste) transposition. Many ISEs do not carry additional genes, but their insertion can disrupt genes or alter expression by providing promoters, terminators, or regulatory signals. When two ISEs flank a gene, they can form a composite transposon capable of mobilizing the intervening DNA, including antibiotic resistance genes.

Impact and significance: ISEs contribute to genome plasticity, mutations, and rearrangements, influencing adaptation and evolution in microbes. They can facilitate the spread of resistance determinants when associated with larger mobile elements. ISEs are also used in molecular genetics as tools for mutagenesis and genome studies, and their identification and classification are aided by databases and bioinformatic tools that recognize terminal inverted repeats and target-site duplications.

Classification and detection: ISEs are grouped into families based on transposase sequence and structural features, such as IS3, IS4, IS5, IS6, and related families. Detection relies on genome sequencing and annotation, with reference databases guiding identification.