P element

A P element is a transposon that is present specifically in the fruit fly Drosophila melanogaster and is used widely for mutagenesis and the creation of genetically modified flies used for genetic research. The P element gives rise to a phenotype known as hybrid dysgenesis.

P elements were discovered in the 1970s when laboratory strains used since 1905 were compared to wild type flies (i.e. found in nature). It seemed that these P elements had swept through all wild type populations of D. melanogaster subsequent to the isolation of the laboratory strains, which did not contain P elements.

The P element encodes for the protein P transposase and is flanked by terminal inverted repeats which are important for its mobility. Unlike laboratory strain females, wild type females are thought to express an inhibitor to P transposase function. This inhibitor reduces the disruption to the genome caused by the P elements, allowing fertile progeny. Evidence for this comes from crosses of laboratory females (which lack P transposase inhibitor) with wild type males (which have P elements). In the absence of the inhibitor, the P elements can proliferate throughout the genome, disrupting many genes and killing progeny.

The P element is a class II transposon, and moves by a DNA-based "cut and paste" mechanism. The sequence comprises 4 exons with 3 introns. Complete splicing of the introns produces the transposase enzyme, while alternative partial splicing of intron 1 and 2 leaving in only intron 3 encodes the P element repressor. The complete, autonomous P element encodes a transposase enzyme, which recognizes the 31 bp terminal inverted repeats of the P element and catalyzes P element excision and re-insertion. The complete element is 2907 bp; non-autonomous P elements contain an internal deletion of varying length which abolishes transposase production, but such elements can still be mobilized if transposase is encoded elsewhere in the genome. P element insertion and subsequent excision results in the production of 8 bp direct repeats, and the presence of such repeats is indicative of previous P element activity.

...
Wikipedia