The profusion of eukaryotic genomes continues to amaze
geneticists: as low as a few percents of eukaryotic
genome length correspond to protein-coding sequences.
Eukaryotic genes are commonly separated by long
regions, and their coding sequences (exons) are intervened
by non-coding ones (introns), which run to tens of
kilobases. Extensive chromosomal regions free from
genes, intergenic regions and introns contain great
numbers of repetitive DNA sequences, most of which
are mobile genetic elements or transposable elements
(TEs). TEs are divided into two major classes: DNA
transposons and retrotransposons. DNA transposons
encode a transposase enzyme catalyzing the transposon
DNA excision and its integration into a new genomic
location (‘cut and paste’ mechanism). Similar to all other
TEs, DNA transposons are transmitted vertically from
parent to offspring; however, their horizontal transmission
between species (sometimes phylogenetically
distant) is not uncommon. Unlike other TEs, DNA
transposons are found in both eukaryotes and prokaryotes
(for review see Feschotte and Pritham, 2007).
Retrotransposons is the most abundant class of TEs.
The transposition of all such elements involves the ‘copy
and paste’ mechanism including transcription of the TE
gene, reverse transcription of the RNA, and integration
of the resulting DNA into a new genomic location. Long
terminal repeat (LTR) elements represent the beststudied
subclass of retrotransposons. They have a very
wide distribution among eukaryotes, from yeast to human.
Structurally, LTR elements resemble retroviral genomic
copies.
The profusion of eukaryotic genomes continues to amazegeneticists: as low as a few percents of eukaryoticgenome length correspond to protein-coding sequences.Eukaryotic genes are commonly separated by longregions, and their coding sequences (exons) are intervenedby non-coding ones (introns), which run to tens ofkilobases. Extensive chromosomal regions free fromgenes, intergenic regions and introns contain greatnumbers of repetitive DNA sequences, most of whichare mobile genetic elements or transposable elements(TEs). TEs are divided into two major classes: DNAtransposons and retrotransposons. DNA transposonsencode a transposase enzyme catalyzing the transposonDNA excision and its integration into a new genomiclocation (‘cut and paste’ mechanism). Similar to all otherTEs, DNA transposons are transmitted vertically fromparent to offspring; however, their horizontal transmissionbetween species (sometimes phylogeneticallydistant) is not uncommon. Unlike other TEs, DNAtransposons are found in both eukaryotes and prokaryotes(for review see Feschotte and Pritham, 2007).Retrotransposons is the most abundant class of TEs.The transposition of all such elements involves the ‘copyand paste’ mechanism including transcription of the TEgene, reverse transcription of the RNA, and integrationof the resulting DNA into a new genomic location. Longterminal repeat (LTR) elements represent the beststudiedsubclass of retrotransposons. They have a verywide distribution among eukaryotes, from yeast to human.Structurally, LTR elements resemble retroviral genomiccopies.
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