Human telomere sequence

Ambrus, A., Chen, D., Dai, J., Biabs, T., Jones, R.A. and Yang, D. (2006) Human telomeric sequence forms a hybrid-type intramolecular G-quadruplex structure with mixed parallel/antiparallel strands in potassium solution, Nucleic Acids Res., 34, 2723-2735. 

The natural occurrence of G-quadmplex in human telomeric sequences remains unproven, although a recent report provides convincing evidence of their occurrence in Stylonychia lemnae telomeres (80). Nevertheless, the existence of... 

Telomeric repeats from other organisms are also prone to quadruplex polymorphism. The Tetrahymena TG4T2G4T telomeric sequence, for example, may adopt several conformations. This sequence forms two novel G-quadruplex structures in Na -containing solution. In the first structure (head-to-head), the two loops are at one end of the G-tetrad core in the second structure (head-to-tail), the two loops are located on opposite ends of the G-tetrad core. In contrast to the human telomere sequence, the proportions of the two forms are similar for a wide range of temperatures their unfolding rates are also similar, with an activation enthalpy of 37 kcal mol . The (G4T4) sequence may also interconvert between parallel and antiparallel structures. 

The human telomeric sequence is not the only one forming different intramolecular quadruplexes. The c-myc quadruplex ( Pu27 ) may form at least two... 

A perylene derivative called PIPER was the first example of a small ligand behaving as a driver in the assembly of quadruplex structures.Gel-shift experiments demonstrate that PIPER can dramatically accelerate the association of a DNA oligomer containing two tandem repeats of the human telomeric sequence (TTAG3) into di- and tetrameric G-quadruplexes. In... 

Figure 10 Structure of intramolecular G-quadruplexes formed by the human telomeric sequence (a-c) in Na solution (d-f) in a -containing crystalf (a, d) Schematic, (b, e) side, and (c,f) top views...

The NMR structure of the monomolecular G-quadruplex formed by (almost) four repeats of the human telomere sequence, d[AGGG(TTAGGG)3], in the presence of Na" ions was reported several years ago. It comprises a core of three G-quartets held together by strands in alternating orientations (Figure 7). This results in two lateral and one diagonal d(TTA) loop that are positioned at the G-quartet ends. This monomolecular G-quadruplex is stabilized by three... 

Attempts to determine the high-resolution structure of the 22-mer human telomeric sequence G-quadruplex in the presence of ions by NMR in solution have been unsuccessful because of the presence of multiple conformations. The crystal structure of the related bimolecular G-quadruplex formed by the sequence d(TAGGGTTAGGGT) in the presence of has... 

Structural model of the complex of the 3,6,9-trisubstituted acridine ligand (3) with the intramolecular basket quadruplex structure of the human telomeric sequence, (a) End-stacking with the terminal G-tetradpermits the substituent at the 9-position to interact with the flexible TTA loop structure in a specific manner, (b) X-ray structure of the complex of a di-substituted aninoalkylamido acridine (4) with the dimeric hairpin quadruplex structure derived from the Oxytricha nova sequence d(GGGGTTTTGGGG)2. The drug end-stacks and interacts extensively with the thymine loop ((a) Adapted from ref 25 and (b) from RCSB Protein Data Bank co-ordinates ILIH (ref 49)). 

Fig. 6 Vertical lEs (in eV) of B-form stacked contiguous guanines and the 5 -TTAGGG-3 human telomere sequence...

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