Crystallization and preliminary investigations on a telomeric repeat sequence C(4)A(2)C(4)A(2)

Repeat units based on the telomeric sequence of the ciliated protozoan Tetr ahymena, d(C(4)A(2))(2), have been crystallized. Cytosine-rich DNA stretche s are known to reside in telomeres and centromeres of eukaryotic chromosome s, playing crucial roles in the structural stability of the chromosome in a ddition to their connection with cancer and aging. Preliminary investigatio ns on the telomeric repeat sequence C(4)A(2)C(4)A(2) from CD studies and X- ray crystal data suggest it to be a right-handed interdigitated tetraplex s tructure with hemiprotonated C.C+ base pairs. The molecules appear to be pa cked one on top of another forming a discontinuous helix along c simulating a poly-C fibre, an arrangement which maximizes the number of cytosines sta cked.