Transposition of some transposable elements occurs by a non-replicative, "cut-and-paste" mechanism. First, the transposase makes a double-stranded cut in the donor DNA at the ends of the transposon and makes a staggered cut in the recipient DNA. Each end of the donor DNA is then joined to an overhanging end of the recipient DNA. DNA polymerase fills in the short, overhanging sequences, resulting in a short, direct repeat on each side of the transposon insertion in the recipient DNA. A cartoon of this process is shown below.
This process results in loss of the transposon from the donor DNA and insertion of the transposon into the recipient DNA. Unlike replicative transposon, the transposon is not "duplicated" in the process. However, because transposition often occurs after replication of the donor DNA molecule, it is not possible to determine if a transposon moves by a non-replicative mechanism by simply looking for loss of the transposon at the original site. For example, in the cartoon shown below the transposon moves by non-replicative transposition, but because of DNA repair or recombination a copy of the transposon is still observed in the original site.
Non-replicative transposition followed by either (a) repair or (b) loss of the donor strand.
Because DNA repair and recombination can obscure the simplest feature of non-replicative transposition, solid experimental evidence for this mechanism of transposition was difficult to obtain. The definative experiment proving this mechanism for transposon Tn10 was done by Bender and Kleckner. The experiment involves several steps:
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Last modified October 15, 2003