K+ and Na+-induced self-assembly of telomeric oligonucleotide d(TTAGGG)n

The telomeric DNA oligomers, d(TTAGGG)(n), where n=1, 2, 4, could self-associate into the multi-stranded structures in appropriate condition and exhibited a different CD spectra. The present of Na+ was more advantage to facilitate the formation of anti-parallel conformation, but the present of K+ enhanced their thermal stability. Spectroscopic analysis of 3, 3'-diethyloxadicarbocyanine (DODC) showed the formation of hairpin quadruplex structures for d(TTAGGG)(2) and d(TTAGGG)(4), but d(TTAGGG) could not. The four-stranded tetraplexes and branched nanowire formed in the present of K+ or Na+ alone were observed by atomic force microscopy (AFM). The ability to self-assemble of d(TTAGGG)(n), into four-stranded tetraplexes and nanowires depends strongly on the number of repeating units and ionic environment. A model to explain how these structures formed is proposed.