G-quadruplex

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G-quadruplex

Telomer-structure

G-quadruplex

A G-quadruplex (also known as a G4 DNA) is a secondary structure formed in nucleic acids by sequences that are rich in guanine. These structures are characterized by the stacking of guanine tetrads, which are square planar arrangements of four guanine bases. G-quadruplexes can form in DNA, RNA, and other guanine-rich sequences and are stabilized by the presence of monovalent cations such as potassium (K+) or sodium (Na+).

Structure

G-quadruplexes are formed by the stacking of guanine tetrads, which are held together by Hoogsteen hydrogen bonds. Each guanine tetrad consists of four guanine bases arranged in a square planar configuration. The guanine bases in a tetrad are connected by Hoogsteen hydrogen bonds, which are different from the Watson-Crick hydrogen bonds that typically stabilize DNA double helices.

The overall structure of a G-quadruplex can vary depending on the sequence and conditions. G-quadruplexes can adopt different topologies, including parallel, antiparallel, and hybrid structures. The loops connecting the guanine tetrads can also vary in length and sequence, contributing to the diversity of G-quadruplex structures.

Biological Significance

G-quadruplexes are found in various regions of the genome, including telomeres, promoter regions of genes, and ribosomal RNA genes. They are believed to play important roles in the regulation of gene expression, maintenance of genome stability, and the protection of chromosome ends.

Telomeres

In telomeres, G-quadruplex structures are thought to protect chromosome ends from degradation and prevent the activation of DNA damage response pathways. The formation of G-quadruplexes in telomeres can inhibit the activity of telomerase, an enzyme that extends telomeres, thereby influencing cellular aging and cancer development.

Gene Regulation

G-quadruplexes in promoter regions can regulate gene expression by influencing the binding of transcription factors and other regulatory proteins. The formation of G-quadruplex structures in these regions can either enhance or repress the transcription of specific genes, depending on the context.

Detection and Study

Various techniques are used to detect and study G-quadruplexes, including circular dichroism spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and X-ray crystallography. These methods provide insights into the structure, stability, and dynamics of G-quadruplexes.

Potential Therapeutic Applications

G-quadruplexes are considered potential targets for therapeutic intervention, particularly in the context of cancer. Small molecules that stabilize or destabilize G-quadruplex structures are being investigated for their potential to modulate gene expression and inhibit the activity of telomerase in cancer cells.

Related Pages

• DNA
• RNA
• Telomere
• Gene expression
• Transcription factor
• Telomerase
• Circular dichroism
• Nuclear magnetic resonance spectroscopy
• X-ray crystallography