Tn4

Tn4 is a bacterial transposable element, a mobile genetic element that can move within and between DNA molecules such as chromosomes and plasmids. It is one of several transposons identified in the Tn3 family and has been studied as a model for understanding transposition mechanisms in bacteria. As with many transposons, Tn4 typically contains genes encoding enzymes required for its movement, commonly including a transposase (tnpA) and a resolvase (tnpR), and is flanked by inverted terminal repeats. The element often includes a res or similar site that participates in the resolution of cointegrates formed during transposition.

Structure and mechanism: Tn4 elements generally rely on a transposition system that can generate DNA rearrangements, such as cointegration with plasmids or other replicons. The transposition process may involve replicative or non-replicative pathways, depending on the specific element and host context, and commonly produces a target-site duplication at the insertion site. The resolvase and res-like sites regulate recombination events during transposition, contributing to the element’s mobility and stability.

Antibiotic resistance and cargo: Many derivatives of Tn4 carry antibiotic resistance determinants, and the exact cargo can vary among isolates. This cargo can spread resistance genes within a bacterial population when the transposon transposes onto plasmids or other mobile elements.

Discovery and significance: Tn4 was described in studies of bacterial genome plasticity and resistance gene transfer. It remains a reference example for the study of transposition mechanisms, genome rearrangements, and the horizontal spread of antibiotic resistance among bacteria.

See also: transposon, Tn3 family transposons, antibiotic resistance genes.