Four-stranded intercalated cytosine-rich molecules: Novel insights into DNA structure and stability

DNA fragments with stretches of cytosine residues can form four-stranded in tercalated i-DNA molecules stabilized by hemiprotonated cytosine . cytosine (+) (C . C+) base pairs. Intriguing features of this motif are the accomoda tion of base stacking that is unfavorable due to electrostatic repulsion an d the close approach of phosphates in narrow grooves of the molecule. Unusu al sources of stability in this structure-involve sugar-base stacking and C H-O interribose short contacts between the backbones of adjacent strands.