Tn10

Tn10 is a well-studied bacterial transposon known for carrying tetracycline resistance. It was identified in Escherichia coli and other Enterobacteriaceae and is often cited as a classic model for understanding transposition and antibiotic resistance gene mobility.

Structure and composition: Tn10 is a composite transposon formed by two copies of the IS10 insertion sequence flanking a tetracycline resistance determinant. The resistance region typically includes the tetA gene, which encodes an efflux-based tetracycline transporter, and the tetR gene, which encodes a regulator that represses tetA expression in the absence of tetracycline. The ends of Tn10 are associated with IS10 inverted repeats, and the transposon can insert into various genomic locations, including plasmids and chromosomes.

Mobility and mechanism: Transposition of Tn10 is mediated by the IS10-encoded transposase. The process inserts Tn10 into new sites and commonly creates short direct repeats at the target site as a consequence of integration. Tn10 movement can occur within genomes or between plasmids, facilitating the spread of tetracycline resistance among bacterial populations.

Resistance and regulation: In the absence of tetracycline, TetR represses tetA expression, minimizing fitness costs. When tetracycline is present, derepression leads to TetA-mediated efflux and increased resistance. This regulatory arrangement makes Tn10 a representative example of how resistance genes are controlled in response to antibiotic exposure.

Significance: Tn10 has played a central role in research on transposable elements and antibiotic resistance. It serves as a model system for studying transposase activity, regulatory control, and the genetic mobility of resistance determinants, as well as a tool in genetic engineering and mutagenesis studies.