DNA transposition
= DNA transposition
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<DNA transposition> is the relocation or insertional copying of a defined <DNA> segment through the action of transposition machinery. The <DNA transposon> is the mobile sequence; <DNA transposition> is the process. In a DNA-mediated system, <transposase> recognizes the relevant ends and coordinates their chemical processing and transfer into target <DNA>. Individual systems differ in whether a donor copy is removed or retained.<A unified classification system for eukaryotic transposable elements by Thomas Wicker and others>[DNA-intermediate classification and mechanistically distinct classII groups]{ref}
The <Tn5> system reveals how two ends can be coordinated. A 2000 structure of <Tn5 transposase> bound to transposon-end <DNA> showed two <protein subunits> organizing the ends into catalytic positions. Each end contacted both subunits, and the structural model explained how end recognition and cleavage could involve different subunits.<Three-dimensional structure of the Tn5 synaptic complex transposition intermediate by D. R. Davies and others>[Abstract, dimeric DNA-end complex and trans-acting cleavage geometry]{ref}
For a bookkeeping example, label a mobile segment `X`. An excision assay can establish that the donor junction changed from `A-X-B` to a repaired arrangement lacking `X`. That observation alone does not locate `X` elsewhere. A new recipient junction containing `X` establishes an additional event. Measuring <DNA transposition> therefore requires distinguishing end recognition, cleavage, target insertion and subsequent <DNA repair>, rather than treating any one signal as proof of every step.