The P element or the P-factor is a DNA transposon, which is found in the fruit fly Drosophila melanogaster and is often used in science to mutagenesis. It can change with the help of a transposase its genomic locus.


The P element is a 2907 base pair long DNA sequence, and has at its ends two 31bp - long opposite repeat sequences ( inverted repeats ) and two - 11bp long direct repeats, which serve as a recognition sequence for the transposase. It contains four exons, encoding a transposase, such that it is an autonomous element P. The approximately 2500 bp - long pre-mRNA is spliced ​​into mRNA and then translated. In the germ line, all three contained the intron between exons from the pre-mRNA are cut out, so that a complete translation of the approximately 87 kDa transposase is possible.

An alternative splicing causes somatic cells in that the third intron ( between exon 3 and 4) will remain in the mRNA, which translation is terminated in this intron, and a non-active ( truncated ) transposase obtained. This polypeptide is 66 kDa in size and accumulates due to its longevity (also) in the germ cells. By the time it competes successfully there with the transposase and thus functions as a repressor her. The result is a more stable genotype in the gonads. Drosophila strains having P- elements, are referred to as "P- strains ", the others as " M- strains ".


The P element is a very successful transposon. To assign research indicates that there has been only in the 1920s to D. melanogaster. In 2000, however, no M strains in the open wilderness could be detected. The P element is identical in sequence to elements of evolutionarily distant Drosophila willi toni- group, suggesting the infection by horizontal gene transfer by a species of this group. Thus, the P- strain has " auskonkurriert " in 80 years, the entire populations of Drosophila melanogaster.


If you cross a male of a P- strain with a female of a M- stem, so lacking in the newly emerged female germline cells of the repressor and the P- element jumps in a very high rate, so there will be mutations. One crosses the other hand, an M- male with a P- females, normal larvae emerge because the eggs so have the repressor. This effect is known as Hybriddysgenese.

P element mutagenesis

In the genetic engineering can use the P element to generate mutations and to make then molecularly visible.

In addition two strains are grown: the log 1 has a modified P element, wherein the transposase has been replaced by a marker gene. Master 2 has a P element with a transposon, however, are the inverted repeats defective, allowing the item to photos, but it can form the transposase not jump. This talk is also jump- starter - element ( Js ).

Now you cross the two strains, as in the cells of the filial generation the transposase of stem 2 is expressed and this can jump the marker P- element of stem 1. The marker indicates that a transposition has taken place and the chromosomal region where it has jumped. When a gene is taken, it can be the basis of the mutation and the marker gene localize genes.

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