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Identifying and predicting sequences which have the capacity to form quadruplexes is an important tool in further understanding their role. Generally, a simple pattern match is used for searching for possible intrastrand quadruplex forming sequences: d(G 3+ N 1-7 G 3+ N 1-7 G 3+ N 1-7 G 3+), where N is any nucleotide base (including guanine). [78]
It is possible that these sequence stretches form G-quadruplex like structures, which can suppress the expression of the related genes. The complementary cytosine rich sequences, on the other strand, may adopt another similar four stranded structure, the i-motif, stabilized by cytosine:cytosine non-canonical base pairs.
In molecular biology, a guanine tetrad (also known as a G-tetrad or G-quartet) is a structure composed of four guanine bases in a square planar array. [ 1 ] [ 2 ] They most prominently contribute to the structure of G-quadruplexes , where their hydrogen bonding stabilizes the structure.
Hoogsteen pointed out that if the alternative hydrogen-bonding patterns were present in DNA, then the double helix would have to assume a quite different shape. Hoogsteen base pairs are observed in alternative structures such as the four-stranded G-quadruplex structures that form in DNA and RNA.
The G-quartet typically binds monovalent cations such as potassium, while other bases can bind numerous other ligands such as hypoxanthine in a U-U-C-U quadruplex. [17] Along with these functions, the G-quadruplex in the mRNA around the ribosome binding regions could serve as a regulator of gene expression in bacteria. [19]
G-quadruplexes, also known as G4 DNA are secondary structures found in nucleic acids that are rich in guanine. [1] These structures are normally located at the telomeres (the ends of the chromosomes). The G-quadruplex can either be parallel or antiparallel depending on the loop configuration, which is a component of the structure.
I-motif DNA forms from any complementary strand of G-quadruplex forming sequence. G-quadruplexes are helically shaped and found in nucleic acids that are rich in guanine. These secondary structures possess guanine tetrads formed into one of three types of strands: one, two, or four.
Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns that occur in multiple copies throughout the genome.In many organisms, a significant fraction of the genomic DNA is repetitive, with over two-thirds of the sequence consisting of repetitive elements in humans. [1]