DNA sequences {transposon, DNA} can excise themselves and then insert at other genome locations {transposition, DNA}|. Transposons code for enzymes that recognize DNA splice sites.
methylation
Methylation inactivates transposons.
bacteria
Bacteria have Tn3 and Tn10 transposons with DNA insertion sequences (IS). Tn3 transposons code enzymes that act at transposon-resolvase sites to allow recombination, so they copy themselves, place copies at new sites, and leave originals.
bacteria: Agrobacterium
Agrobacterium infects plants with Ti plasmid.
yeast
Yeast has Ty elements, whose delta-element direct repeats have promoters. Ty elements contain reverse transcriptase.
Yeast MAT genes have mating-type alleles. Yeasts have two mating types, a and alpha. After mating, mating type changes to opposite mating type, as HO endonuclease cuts MAT site. a-gene and alpha-gene copies are far from MAT sites. Copies are templates to reconstruct MAT site as opposite mating type {gene conversion} {replicative transposition}.
Yeast sterile (STE) genes code for a and alpha pheromones, which stop cell growth and change cell shape. Pheromones combine both mating types to form diploids, causing yeast to mate. STE proteins are G-protein subunits (STE4) (STE18), protein kinases, and transcription factors (STE12). STE proteins (STE2) (STE3) can bind factors.
maize
Maize has Ac and Ds transposable elements.
retrovirus
Retroviruses have direct repeats with promoters and contain reverse transcriptase to allow transposition.
trypanosome
Trypanosomes use gene conversion to vary surface glycoproteins (VSG).
fruitfly
Drosophila have P elements. Drosophila have copia elements, which have direct repeats with promoters.
Fruitfly P elements and other transposition elements can code for enzymes that recognize DNA splice sites. By opening and closing splice sites, genes {transposon, genetics} {jumping gene} can excise and insert between any two splice sites.
Reverse transcriptase can make DNA {retrotransposon} {retroposon} from RNA, and DNA can insert back into genome at special sites. Virus-gene fragments can copy themselves and insert in genomes. DNA from retrovirus RNA {human endogenous retrovirus} (Hervs) is 1% of human genome.
All species have 750-base to 5000-base sequences that code for enzymes {transposase} that recognize DNA sites just beyond both transposase-gene ends.
process
Sites have 10-base to 40-base inverted repeats. Transposase enzymes recognize inverted repeats and cut out transposase-gene sequence between sites. Transposases recognize inverted repeat at other locations in genomes, plasmids, or phages and cut sequence to place transposase-gene sequence in those locations. If two transposons are near each other, transposases can cut at the farthest ends and both transposons, and any DNA between them {complex transposon}, can transpose as one sequence to inverted repeats at other locations.
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Date Modified: 2022.0225