DNA transposition


DNA transpositionsearch for term

Barbara McClintock spent many years patiently studying the behaviour of unusual genetic elements in maize. She concluded that these elements were, in fact, mobile. Her work, all the more amazing because much of it was carried out before the structure of DNA was solved, was largely ignored until the mid 1970s when similar elements were discovered in bacteria. The major difference of class II transposons from retrotransposons is that their transposition mechanism does not involve an RNA intermediate. Class II transposons usually move by a mechanism analogous to cut and paste, rather than copy and paste, using the transposase enzyme. Different types of transposase work in different ways. Some can bind to any part of the DNA molecule, and the target site can therefore be anywhere, while others bind to specific sequences. Transposase makes a staggered cut at the target site producing sticky ends, cuts out the transposon and ligates it into the target site. A DNA polymerase fills in the resulting gaps from the sticky ends and DNA ligase closes the sugar-phosphate backbone. This results in target site duplication and the insertion sites of DNA transposons may be identified by short direct repeats (a staggered cut in the target DNA filled by DNA polymerase) followed by inverted repeats (which are important for the transposon excision by transposase). (http://en.wikipedia.org/wiki/Transposon )