|MoBio||Transpositional Recombination||Chapter 8|
Transpositional recombination is a process in which a mobile element is inserted into a target DNA. It may occur by one of two mechanisms: (1) directly as DNA, (2) through RNA. The mobile elements that transpose through DNA are called transposons and those via RNA are referred to as retrotransposons. Some examples are given in the following figure.
Figure 8-D-8. Classification of mobile elements.
Mechanisms of transpositional recombination
The transpositional recombination as shown above involves DNA recombination whose mechanism is explained in the following figure.
Figure 8-D-10. Mechanism of DNA recombination in transposition.
In bacteria, the target DNA is cut by transposase, producing sticky ends (single strands, easy to pair with complementary sequences). The transposase also has ligase activity which may ligate the intermediate DNA of transposons. The gaps at sticky ends are filled by DNA polymerase, generating direct repeats.
Other organisms are expected to use the same mechanism to insert the DNA intermediates of either transposons or retrotransposons into target DNA. The direct repeats generated by this mechanism is found in ALL mobile elements.
In recombinant DNA technology, a DNA fragment is inserted into a target DNA by a slightly different mechanism, which is explained in Chapter 9.