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 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 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. The ribosomal RNA and transfer RNA genes belong to the class of middle repetitive DNA.

See also

• inverted repeat

References

1. 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. 8 (1 ed.). Springer. pp. 133–144. ISBN 978-1-84800-254-8.