Four-Repeat Human Telomeric Sequence

The four-repeat human telomeric d[AGGG(TTAGGG)3] sequence was shown to form an intramolecular G-quadruplex in Na solution, in which guanines around each tetrad are syn syn anti anti, loops are successively edgewise-diagonal-edgewise and each G-tract has both a parallel and an antiparallel adjacent strands [Figure lO(a-c)]. By contrast, the crystal structure of the same... 

Figure 11 Structures of the (3+1) core-containing G-quadruplexes formed by (a) the four-repeat Tetrahymena telomeric d[ (TTGGGG)4] sequence in Na solu-tion, (b) the three-repeat human telomeric d[GGG(TTAGGG)2T] sequence in Na solution,and (c) the four-repeat human telomeric d[TAG-GG(TTAGGG)s] sequence in solution ...

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... 

A. The G-quadruplex formed by d[AGGG(TTAGGG)3] is of particular interest because it represents four units of the human telomere repeat sequence. Details of the crystal structure formed by this sequence in the presence of ions and in the presence of Na ions are discussed below in Section 4.6. The crystal structure of the bimolecular G-quadruplex adopted by the dodecamer sequence d(TAGGGTTAGGGT), also derived from the human telomere repeat sequence, has been determined and similarly contains K" ions coordinated between adjacent G-quartets (PDB ID 1K8P). ... 

---