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 edit
There are several types of repeated sequences :
- Interspersed (or dispersed) DNA repeats (interspersed repetitive sequences) are copies of transposable elements interspersed throughout the genome.
- Flanking (or terminal) repeats (terminal repeat sequences) are sequences that are repeated on both ends of a sequence, for example, the long terminal repeats (LTRs) on retroviruses. Direct terminal repeats are in the same direction and inverted terminal repeats are opposite to each other in direction.
- Tandem repeats (tandem repeat sequences) are repeated copies which lie adjacent to each other. These can also be direct or inverted repeats.[citation needed] The ribosomal RNA and transfer RNA genes belong to the class of middle repetitive DNA.
Microsatellite DNA edit
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 edit
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 edit
References edit
- ^ a b c Ussery, David W.; Wassenaar, Trudy; Borini, Stefano (2008-12-22). "Word Frequencies, Repeats, and Repeat-related Structures in Bacterial Genomes". Computing for Comparative Microbial Genomics: Bioinformatics for Microbiologists. Computational Biology. Vol. 8 (1 ed.). Springer. pp. 133–144. ISBN 978-1-84800-254-8.
- ^ a b Richard, G. F. (2021). "The Startling Role of Mismatch Repair in Trinucleotide Repeat Expansions". Cells. 10 (5): 1019. doi:10.3390/cells10051019. PMC 8145212. 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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