The pH-dependent stability of DNA i-motif

Abstract

As the carrier of genetic codes, deoxyribonucleic acid(DNA) has many structures besides B-DNA. Among these structures, the tetraplex structures (i-motif and G-quadruplex) have been frequently studied recently. These C-rich sequences which are likely to form i-motifs are usually found in the telomeric DNA at the chromosome ends, relating to cancer and aging, etc. In this thesis, we used force spectroscopy to study the stability and unfolding pathway of single intramolecular i-motif structure, formed on the human telomeric sequence 5?-(CCCTTA)3CCC in different pH condition. We measured the unfolding force distributions and unfolding step size distributions at different loading rates and different pH conditions. We found that the unfolding force distributions strongly depend on pH conditions. In certain pH and loading rate conditions, the unfolding forces distribution of i-motif show two peaks, indicating that the unfolding of i-motif not a simple two-state pathway.