Telomeric repeat-containing RNA, a non-coding RNA molecule, has recently been 
found in mammalian cells. The detailed structural features and functions of the 
telomeric RNA at human chromosome ends remain unclear, although this RNA 
molecule may be a key component of the telomere machinery. In this study, using 
model human telomeric DNA and RNA sequences, we demonstrated that human 
telomeric RNA and DNA oligonucleotides form a DNA-RNA G-quadruplex. We next 
employed chemistry-based oligonucleotide probes to mimic the naturally formed 
telomeric DNA-RNA G-quadruplexes in living cells, suggesting that the process of 
DNA-RNA G-quadruplex formation with oligonucleotide models of telomeric DNA and 
RNA could occur in cells. Furthermore, we investigated the possible roles of 
this DNA-RNA G-quadruplex. The formation of the DNA-RNA G-quadruplex causes a 
significant increase in the clonogenic capacity of cells and has an effect on 
inhibition of cellular senescence. Here, we have used a model system to provide 
evidence about the formation of G-quadruplex structures involving telomeric DNA 
and RNA sequences that have the potential to provide a protective capping 
structure for telomere ends.