Abstract: Telomeric DNA and TERRA(Telomeric repeat-containing RNA, a non-coding telomeric RNA) are consisted of tandem repeats rich in successive guanines, both can form G-quadruplex structures to inhibit the telomere extension by the telomerase and prevent the infinite proliferation of cancer cells. An intermolecular G-quadruplex complex can be formed between telomeric DNA and TERRA and has some functions, but little has been reported about this. Nuclear magnetic resonance(NMR) experiment showed that both human and Giardia lamblia telomeres formed DNA-RNA intermolecular G-quadruplex complexes. Based on the circular dichroism(CD) spectrum and NMR titration, it was found that, due to sharing the same sequence, a short sequence of TERRA was able to compete with and eventually replace the corresponding short telomeric DNA sequence within a DNA-DNA parallel-antiparallel hybrid intermolecular G-quadruplex complex. The resulting DNA-RNA G-quadruplex complex is induced into a full parallel conformation. In addition, the DNA-RNA G-quadruplex complex is more stable than the DNA-DNA G-quadruplex complex. Study on the structure and properties of telomeric DNA-RNA G-quadruplex complex can provide new insights into the interacting mode between TERRA and telomeric DNA and the way to maintain telomeric stability by TERRA.

Key words: telomere, DNA-RNA G-quadruplex complex, nuclear magnetic resonance, circular dichroism