Quadruplex

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

Quadruplex

This format revolutionized broadcast television operations and television production , since the only recording medium available to the TV industry until then was Motion picture film. Since most United States network broadcast delays by the television networks at the time used kinescope film that took time to develop, the networks wanted a more practical, cost-effective, and quicker way to time-shift television programming for later airing in Western time zones than the expensive and time-consuming processing and editing of film. Faced with these challenges, broadcasters sought to adapt magnetic tape recording technology already used for audio recording for use with television as well. By the television industry in the US was consuming more film stock than all Hollywood studios combined. This method is called quadrature scanning, as opposed to the helical scan transport used by later videotape formats. The tape ran at a speed of either 7. The cue track was used either as a second audio track, or for recording cue tones or time code for linear video editing. The quadruplex format employs segmented recording; each transversely recorded video track on a 2-inch quad videotape holds one-sixteenth NTSC or one-twentieth PAL [6] field of interlaced video. For NTSC systems, the math suggests 15 transverse head passes, each consisting of 16 lines of video, are required to complete one field. This meant that 2-inch quad did not support "trick-play" functions, such as still, shuttle, and reverse or variable-speed playback. In fact, the quadruplex format could only reproduce recognizable pictures when the tape was playing at normal speed. Most quad machines made later in the s and s by Ampex can play back both low and high-band 2-inch quad tape. Time-shifting of television programming for the Central , Mountain , and Pacific Time Zones by the networks in the s in order to broadcast their programming at the same local time in each time zone using kinescope films was quite a rushed and perilous ordeal. This usually meant the kinescope was aired almost immediately after it came straight out of the developing equipment, still warm from the film dryer.

There have been two recent systematic surveys of the complete human genome sequence, searching for potential unimolecular quadruplex-forming sequences 18 As of now, [ when? Ampex, seeing the impracticality of the prototype BCE and RCA Quadruplex, started to develop a more practical videotape format with tape economy in mind, as well as providing a solution to quadruplex networks' West Coast delay woes, 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. Computational studies and sequencing methods have revealed the prevalence of G4 sequence motifs at gene regulatory regions in various genomes, including in humans. Experiments using chemical, molecular and cell biology methods have demonstrated that G4s exist in chromatin DNA and in RNA, and have linked G4 formation with key biological processes ranging from transcription and translation to genome instability and cancer. In this Review, we first discuss the identification of G4s and evidence for their formation in cells using chemical biology, imaging and genomic technologies. We then discuss possible functions of DNA G4s and their interacting proteins, particularly in transcription, telomere biology and genome instability. Furthermore, we consider the emerging relationships of G4s with chromatin and with RNA modifications.

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Lei M. These ligands can be naturally occurring or synthetic. Analytical Chemistry. The particles are oriented by applying a strong transverse magnetic field during manufacturing after the particles are applied but before the tape is baked to fix the particles in place. A survey of all 16 genes in the human gene database has found that there is a significant correlation between quadruplex sequence occurrence and classes of gene 80 , with proto-oncogenes having a high quadruplex-forming potential compared with a low potential for tumour-suppressor genes. Small single-base loops are the most common and loops which are made up of guanines in the centre of a sequence are abundant e. An analysis, restricted to loops with differing numbers of thymine residues, used molecular dynamics in conjunction with biophysical measurements 59 , and has concluded that quadruplexes with three T 1 loops are constrained to only form parallel topologies, whereas quadruplexes with three T 2 loops can form both parallel and anti-parallel topologies in this instance parallel structures are likely to be favoured. Parkinson , Pascale Hazel , Alan K. Olsen C. Arnott S. Petraccone L.

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Cmugelj M. Contents move to sidebar hide. Topology and structure Quadruplex formation has been examined in vitro in a number of non-telomeric sequences Table 4. Crystal structure of parallel quadruplexes from human telomeric DNA. In quadruplexes formed from double-stranded DNA, possible interstrand topologies have also been discussed [21]. Brussels sprout. The bcl-2 oncogene has a major transcriptional promoter sequence ca. Huppert JL, Balasubramanian S The binding of ligands to G-quadruplexes is vital for anti-cancer pursuits because G-quadruplexes are found typically at translocation hot spots. Ranveer Singh purchased a quadruplex apartment? None declared. Chemical and Engineering News. Metal complexes have a number of features that make them particularly suitable as G4 DNA binders and therefore as potential drugs. Data from the c-myc sequences 84 when embedded in plasmids, which are then transfected in cells is strongly indicative of quadruplex formation in a more complex environment than the NMR tube; however, the difficulty of observing endogenous DNA quadruplex structures in live cells is a major challenge for the future. This may be overcome by the use of mutated or modified sequences based on the original G-rich sequence, but which only form a single species in solution environments.