Quadruplex

G-quadruplexes are higher-order DNA and RNA structures formed from G-rich sequences that are built around tetrads quadruplex hydrogen-bonded guanine bases.

In molecular biology, G-quadruplex secondary structures G4 are formed in nucleic acids by sequences that are rich in guanine. The placement and bonding to form G-quadruplexes is not random and serve very unusual functional purposes. The quadruplex structure is further stabilized by the presence of a cation , especially potassium , which sits in a central channel between each pair of tetrads. G-quadruplex structures can be computationally predicted from DNA or RNA sequence motifs, [11] [12] but their actual structures can be quite varied within and between the motifs, which can number over , per genome. Their activities in basic genetic processes are an active area of research in telomere, gene regulation, and functional genomics research.

Quadruplex

Federal government websites often end in. The site is secure. G-quadruplexes are higher-order DNA and RNA structures formed from G-rich sequences that are built around tetrads of hydrogen-bonded guanine bases. Potential quadruplex sequences have been identified in G-rich eukaryotic telomeres, and more recently in non-telomeric genomic DNA, e. The natural role and biological validation of these structures is starting to be explored, and there is particular interest in them as targets for therapeutic intervention. This survey focuses on the folding and structural features on quadruplexes formed from telomeric and non-telomeric DNA sequences, and examines fundamental aspects of topology and the emerging relationships with sequence. Emphasis is placed on information from the high-resolution methods of X-ray crystallography and NMR, and their scope and current limitations are discussed. Such information, together with biological insights, will be important for the discovery of drugs targeting quadruplexes from particular genes. The knowledge that guanine-rich nucleic acids can self-associate has a long history, pre-dating the double helix itself by almost 50 years. For much of that time, the gels formed by such sequences were more of nuisance value than scientific worth. The molecular basis for the association was subsequently determined by fibre diffraction 1 — 3 and biophysical 4 studies using the concept 5 , 6 that the Hoogsteen hydrogen-bonded guanine G -tetrad also termed a G-quartet is the basic structural motif Figure 1a. The synthetic polynucleotides poly dG and poly G were determined in these studies to form four-stranded helical structures Figure 1b with the G-tetrads stacked on one another, analogous to Watson—Crick base pairs in duplex DNA.

Conflict of interest statement. Randazzo A, quadruplex. It is unsurprising that some studies suggest the co-existence of several forms 59quadruplex, 6067especially in view of the ability of quadruplexes with 3 nt loops to readily adopt topologically distinct structures upon small changes in environment or sequence, suggesting quadruplex the various forms are quadruplex.

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Quadruplex

Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Four-stranded G-quadruplex G4 structures form through self-recognition of guanines into stacked tetrads, and considerable biophysical and structural evidence exists for G4 formation in vitro.

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Trends in Biotechnology. Implications for G-quadruplex stabilization. None declared. The NMR structure of the G-quadruplex from the c-myc promoter sequence with five G-tracts 89 shows that the presence of the fifth very short tract can produce unexpected and significant changes in topology compared to analogous sequences with four tracts, so topology and structure prediction for new quadruplexes based on the very small number of known quadruplex structures is probably premature at present. Trends of quadruplex. Science Museum Group Collection. Most quad machines made later in the s and s by Ampex can play back both low and high-band 2-inch quad tape. HERVd: database of human endogenous retroviruses. For therapeutic advances, stabilizing the G-quadruplexes of cancerous cells can inhibit cell growth and replication leading to the cell's death. Download as PDF Printable version.

In molecular biology, G-quadruplex secondary structures G4 are formed in nucleic acids by sequences that are rich in guanine. The placement and bonding to form G-quadruplexes is not random and serve very unusual functional purposes.

Huppert JL, Balasubramanian S The assumption that all G tracts within a quadruplex sequence are identical is true for vertebrate telomeric sequences, but is not always the case for non-telomeric genomic sequences, or even for all telomeric sequences in some lower eukaryotics see Table 1. Dai J. This is reflected in the frequency of occurrence of each loop sequence. In the absence of proteins or small molecules, the equilibrium for vertebrate telomeric DNA has been found 63 to favour duplex over dissociation into quadruplex and i-form motifs the four-stranded arrangements formed by the complementary C-rich strand and organized around cytosine—cytosine base pairs. French images. Cevec M. For instance, quantitative assessments of the thermodynamics of molecular crowding indicate that the antiparallel g-quadruplex is stabilized by molecular crowding. Resolution of the requirement for duplex unwinding in promoter sequences in order for the G-rich strand to transiently become single-stranded, may be achieved by strand scission; it has been recently reported that DNA topoisomerase II produces double-strand breaks in promoter sequences , which could be a suitable mechanism for achieving this. Mar 05, It also seems that differing numbers of guanines in the individual G-tracts results in quadruplexes with asymmetric topologies, which again, are not readily predictable at present. The structures most present in the promoter regions of these oncogenes tend to be parallel-stranded G-quadruplex DNA structures. Cogio S. Video Guides. ISBN