| Abstract
| - We present an NMR study on the structure of a DNA fragment of the human telomere containingthree guanine-tracts, d(GGGTTAGGGTTAGGGT). This sequence forms in Na+ solution a unique asymmetricdimeric quadruplex, in which the G-tetrad core involves all three G-tracts of one strand and only the last3‘-end G-tract of the other strand. We show that a three-repeat human telomeric sequence can also associatewith a single-repeat human telomeric sequence into a structure with the same topology that we name(3 + 1) quadruplex assembly. In this G-quadruplex assembly, there are one syn·syn·syn·anti and two anti·anti·anti·syn G-tetrads, two edgewise loops, three G-tracts oriented in one direction and the fourth orientedin the opposite direction. We discuss the possible implications of the new folding topology for understandingthe structure of telomeric DNA, including t-loop formation, and for targeting G-quadruplexes in the telomeres.
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