Dyad symmetry
Encyclopedia
In genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

, dyad symmetry refers to two areas of a DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 strand whose base pair sequences are inverted repeat
Inverted repeat
An inverted repeat is a sequence of nucleotides that is the reversed complement of another sequence further downstream.For example, 5'---GACTGC....GCAGTC---3'. When no nucleotides intervene between the sequence and its downstream complement, it is called a palindrome. Inverted repeats define the...

s of each other. They are often described as palindromes.

For example, the following shows dyad symmetry between sequences GAATAC and GTATTC which are reverse complements of each other.
...GAATAC...CTG...GTATTC...

Involvement in transcription

Since the two reverse complementary sequences will fold and base-pair with each other, the sequence of bases between them form a hairpin loop. This structure is thought to destabilize the binding of RNA polymerase enzyme to DNA (hence terminating transcription). Dyad symmetry is known to have a role in the rho dependent method of transcription termination in E. coli. Regions of dyad symmetry in the DNA sequence stall the RNA polymerase enzyme as it transcribes them.

Involvement in prophage integration

Temperate bacteriophage
Bacteriophage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...

s integrate into the host genome at specific interrupted dyad symmetry sequences using the phage encoded enzyme integrase (see prophage integration).

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