Chemistry Reference
In-Depth Information
3.5 Bimolecular G - Quadruplexes of Analogues of
the
Oxytricha
Telomere Repeat
The NMR structure of the G-quadruplex formed by d(G
4
T
4
G
4
) in the presence of
NaCl was one of the fi rst G-quadruplex structures determined at high resolution.
96,97
DNA oligonucleotide d(G
4
T
4
G
4
), which contains 1.5 repeats of the
Oxytricha
tel-
omere folds into a well-behaved bimolecular G-quadruplex. The topology, shown in
Figure 3.6a, exhibits a symmetrical bimolecular G-quadruplex with four G-quartets
and thymine loops at opposite ends of the G-quartets. The glycosidic torsion angles
are
syn
-
syn
-
anti
-
anti
around each G-quartet. Guanines are alternately in
syn
and
anti
conformations along each strand. Adjacent strands are alternately in parallel
and antiparallel orientations. The two T
4
loops span across diagonals of the outer
G - quartets.
97,236
NMR solution studies showed that d(G
4
T
4
G
4
) adopts the same
Figure 3.6
(Plate 4)
Topology of analogues of the
Oxytricha nova
telomere repeat sequence:
(a) the structure of bimolecular d[(G
4
T
4
G
4
)
2
] quadruplex was one of the fi rst high resolution
structures of G-quadruplexes determined;
96
(b) unique folding topology of d[(G
3
T
4
G
4
)
2
] with
(3 + 1) strand orientations;
244
(c) topology of d[(G
4
T
4
G
3
)
2
];
243
(d) asymmetric structure of
d[(G
3
T
4
G
3
)
2
]
238
(See colour plate section)
