Guanine tetrad

See also: G-quadruplex

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.^[3][4] Usually, there are at least two guanine tetrads in a G-quadruplex, and they often feature Hoogsteen-style hydrogen bonding.^[1]

Left: A guanine tetrad featuring a central cation
Right: Three guanine tetrads contributing to the structure of a G-quadruplex

Guanine tetrads are formed by sequences rich in guanine, such as GGGGC.^[5] They may also play a role in the dimerization of non-endogenous RNAs to facilitate the replication of some viruses.^[5] Guanine tetrads dimerize through their 5' ends since it is more energetically favorable.^[6]

They can be stabilized by central cations, such as lithium, sodium, potassium, rubidium, or caesium.^[7][8] However, they still form a variety of different structures.^[1] Guanine tetrads are not always stable, but the sugar-phosphate backbone of DNA can assist in stability of the guanine tetrads themselves.^[1] Guanine tetrads are more stable when stacked, as intermolecular forces between each layers help stabilize them.^[9]

Guanine tetrads can also influence recombination, replication, and transcription.^[1][2] For instance, guanine tetrads are found in the promoter region of the Myc family of oncogenes.^[10] They also function in immunoglobulin class switching and may play a role in the genome of HIV.^[11] Guanine tetrads appear frequently in the telomeric regions of DNA.^[3]

See also

• G-quadruplex
• Hoogsteen base pair
• Heterochromatin
• Regulation of gene expression
• Guanine
• Telomere