Tn5 is a bacterial DNA transposon used as a model for how mobile DNA ends are recognized, processed and inserted into another DNA molecule. The element is a DNA sequence; Tn5 transposase is the protein that supplies its catalytic machinery. The assembled enzyme–DNA complex is a transpososome.
A 2000 structure determined Tn5 transposase bound to transposon-end DNA at resolution. Two protein subunits contacted each end and positioned the ends in the active sites. The geometry explained how recognition by one subunit and cleavage by the other could coordinate the reaction.[ref]
Three-dimensional structure of the Tn5 synaptic complex transposition intermediate by D. R. Davies and others. Abstract, DNA-end complex, dimeric arrangement and catalytic geometry
This machinery became useful beyond studying a naturally mobile element. The 2013 ATAC-seq study used transposition to introduce sequencing adaptors into native chromatin, generating fragments informative about chromatin accessibility and molecular organization.[ref]
Transposition of native chromatin for fast and sensitive epigenomic profiling of open chromatin, DNA-binding proteins and nucleosome position by Jason D. Buenrostro and others. Abstract, transposition into native chromatin and accessible-region profiling
The distinction between element and enzyme clarifies the tool. A DNA fragment processed by a prepared Tn5 transposase complex need not itself contain the gene encoding the enzyme. Observing a tagged fragment therefore establishes an enzyme-mediated event, rather than showing that every product has acquired autonomous transposition machinery. The sequence, catalyst and experimental readout describe different parts of the system.
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