Direct repeat
Direct repeats are a type of genetic sequence that consists of two or more repeats of a specific sequence.[1] In other words, the direct repeats are nucleotide sequences present in multiple copies in the genome. Generally, a direct repeat occurs when a sequence is repeated with the same pattern downstream.[1] There is no inversion[clarification needed] and no reverse complement associated with a direct repeat. It may or may not have intervening nucleotides. The nucleotide sequence written in bold characters signifies the repeated sequence.
- 5´ TTACGnnnnnnTTACG 3´
- 3´ AATGCnnnnnnAATGC 5´
Linguistically, a typical direct repeat is comparable to saying "bye-bye".[1]
Types
There are several types of repeated sequences :
- Interspersed (or dispersed) DNA repeats (interspersed repetitive sequences) are copies of transposable elementsinterspersed throughout the genome.
- Flanking (or terminal) repeats (terminal repeat sequences) are sequences that are repeated on both ends of a sequence, for example, the retroviruses. Direct terminal repeats are in the same direction and inverted terminal repeats are opposite to each other in direction.
- genes belong to the class of middle repetitive DNA.
Microsatellite DNA
A tract of repetitive DNA in which a motif of a few base pairs is tandemly repeated numerous times (e.g. 5 to 50 times) is referred to as microsatellite DNA. Thus direct repeat tandem sequences are a form of microsattelite DNA. The process of DNA mismatch repair plays a prominent role in the formation of direct trinucleotide repeat expansions.[2] Such repeat expansions underlie several neurological and developmental disorders in humans.[2]
Homologous recombination
In directly repeated sequences of the tobacco plant genome, DNA double-strand breaks can be efficiently repaired by homologous recombination between the repeated sequences.[3]
See also
References
- ^ ISBN 978-1-84800-254-8.
- ^ PMID 33925919.
- ^ Siebert R, Puchta H. Efficient repair of genomic double-strand breaks by homologous recombination between directly repeated sequences in the plant genome. Plant Cell. 2002 May;14(5):1121-31. doi: 10.1105/tpc.001727. PMID: 12034901; PMCID: PMC150611
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