= Transposase
A <transposase> is an <enzyme> that catalyzes steps in <DNA transposition>, the movement of a <transposable element> between DNA locations. The mobile <DNA> sequence and its enzyme are distinct objects: the DNA carries recognition features, while the protein supplies catalytic and binding functions. Different <DNA transposons> use different reaction pathways, so transposase is a functional category rather than the name of one universal molecular machine.<A unified classification system for eukaryotic transposable elements by Thomas Wicker and others>[Page 973, classification by transposition intermediate and mechanism]{ref}
A structural example is <Tn5 transposase>. A 2000 study determined a $2.3\,\text{Å}$ structure of the enzyme bound to transposon-end <DNA>. The complex was a <dimer>, with both protein subunits contacting each DNA molecule. Binding by one subunit and cleavage by the other showed that recognizing two DNA ends is a coordinated assembly problem.<Three-dimensional structure of the Tn5 synaptic complex transposition intermediate by D. R. Davies and others>[Abstract, dimeric assembly and transposon-end contacts]{ref}
This enzyme–DNA assembly is a <transpososome>. The structure connects the geometry of the recognized ends to the <active sites> that process them. It does not mean that a lone protein bound to an arbitrary DNA fragment would reproduce the entire reaction.
A conceptual two-component example separates coding capacity from mobility. One DNA element contains recognizable ends but lacks a working enzyme gene. Another source supplies the compatible <transposase>. The first is a <non-autonomous transposable element>: inability to produce its own enzyme does not by itself mean that it cannot be mobilized in that cellular setting.<Vectors for P element-mediated gene transfer in Drosophila by G. M. Rubin and A. C. Spradling>[Abstract, non-autonomous P-element vectors]{ref}
Recognition, cutting, joining to a new target and subsequent host <DNA repair> are experimentally distinguishable events. An assay that detects only the initial cleavage establishes one part of <DNA transposition>, not automatically successful integration at a new site.
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