Crystallization and preliminary investigations on a telomeric repeat sequence C₄A₂C₄A₂

Repeat units based on the telomeric sequence of the ciliated protozoan Tetrahymena, d(C₄A₂)₂, have been crystallized. Cytosine-rich DNA stretches are known to reside in telomeres and centromeres of eukaryotic chromosomes, playing crucial roles in the structural stability of the chromosome in addition to their connection with cancer and aging. Preliminary investigations on the telomeric repeat sequence C₄A₂C₄A₂ from CD studies and X-ray crystal data suggest it to be a right-handed interdigitated tetraplex structure with hemiprotonated CC⁺ base pairs. The molecules appear to be packed one on top of another forming a discontinuous helix along c simulating a poly-C fibre, an arrangement which maximizes the number of cytosines stacked.