Transposon families

Prokaryotic Transposable Elements

Prokaryotic transposable elements (TEs) are pivotal in shaping bacterial genome architecture and facilitating horizontal gene transfer. Among these, several well-characterized families—composite transposons, Tn3, Tn7, Tn402, and Tn554—exemplify the diversity of transposition mechanisms and their roles in disseminating adaptive traits such as antibiotic resistance.

Prokaryotic Transposon Families
1. Composite or compound transposon 2. Tn3 family transposons 3. Tn7 family transposons 4. Tn402 family transposons 5. Tn554 family transposons

Composite Transposons

Composite transposons are formed when two insertion sequences (IS elements) flank a central region containing accessory genes, often including antibiotic resistance determinants. The flanking IS elements, which can be in direct or inverted orientation, provide the transposase enzymes necessary for mobilization. A classic example is Tn10, comprising two IS10 elements flanking genes that confer tetracycline resistance. Transposition typically follows a cut-and-paste mechanism, wherein the entire composite structure is excised and inserted into a new genomic location.

Learn more in our chapter: Composite or compound transposon |

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Tn3 Family

The Tn3 family encompasses replicative transposons that transpose via a copy-and-paste mechanism, resulting in the duplication of the transposon. The transposition process involves the formation of a cointegrate intermediate, which is subsequently resolved into separate replicons .

Learn more in our chapter: Tn3 family transposons |

Tn7 Family

Tn7 family transposons are distinguished by their ability to insert into specific genomic sites, notably the attTn7 site located downstream of the glmS gene in many bacteria. This site-specific insertion is mediated by a complex of transposition proteins, including TnsA, TnsB, TnsC, and TnsD. Alternatively, Tn7 can insert into mobile DNA elements such as plasmids via the TnsE pathway, facilitating horizontal gene transfer. Tn7 elements often carry genes conferring antibiotic resistance and have been instrumental in the development of genetic tools due to their predictable insertion patterns.

Learn more in our chapter: Tn7 family transposons |

Tn402 Family

The Tn402 family is closely associated with class 1 integrons, genetic elements that capture and express gene cassettes, frequently encoding antibiotic resistance. Tn402 provides the transposition module for these integrons, enabling their mobilization within and between genomes. The transposition machinery typically includes a transposase and a resolvase, facilitating movement via a replicative mechanism. The integration of Tn402-associated integrons into diverse genomic contexts contributes significantly to the spread of multidrug resistance among pathogenic bacteria.

Learn more in our chapter: Tn402 family transposons |

Tn554 Family

Tn554 family transposons are characterized by their site-specific integration into the radC gene, which is involved in DNA repair. These elements encode three proteins essential for transposition: TnpA, TnpB, and TnpC. Notably, TnpA and TnpB possess a C-terminal motif characteristic of tyrosine recombinases, suggesting a recombination-based transposition mechanism. Tn554 elements often carry genes conferring resistance to antibiotics such as erythromycin and spectinomycin. Their precise integration and excision mechanisms make them valuable models for studying site-specific recombination.

Learn more in our chapter: Tn554 family transposons |

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The Major Transposon Families. The transposons are not to scale. The horizontal black bars above each indicates a length of 2 kb. Transposons are represented as yellow-filled boxes. Genes are represented as arrows within the transposon with the direction of expression indicated by the arrow heads. Transposition-related genes are shown as lavender, resistance genes as red, integron integrase as blue, genes with other functions in pink and hypothetical genes in magenta. Recombination sites are shown in green. 1) A composite or compound transposon, Tn10; 2) A Tn3 family transposon of the Tn3 group, Tn3; 3) A Tn3 family transposon of the Tn21 group, Tn5060; 4) A Tn7 family transposon, Tn7; 5) A Tn402 family transposon, Tn402; 6) A Tn554 family transposon Tn554.