CHED 619

Structural implications of incorporating 6-thioguanine into a DNA quadraplex

Stephen U. Dunham, Matthew A. Davis, and Drew J. Davis. Chemistry, Colby College, 5763 Mayflower Hill, Waterville, ME 04901-8857, fax: 207-872-3804,

At the ends of the human chromosome lies the DNA telomere with the repeating sequence d(AGGGTT)n. While much of the telomere is duplex DNA, the ends are thought to be single strands. These single stranded segments could fold intramolecularly into four-stranded structures stabilized by three G-tetrads. 6-thioguanine is a known anti-cancer agent that is readily incorporated in place of guanine during DNA replication. The replacement of oxygen by sulfur at the O6 position of guanine has been proposed to hinder hydrogen bonding necessary for normal G-tetrad formation and could lead to changes in telomere stability.

The human telomere sequence d[AG3(T2AG3)3] (HT1) was chosen as a control because it has been observed to fold into a quadraplex. HT1 was synthesized and modified by replacing various guanine bases with 6-thioguanine. The control and modified DNAs were purified by HPLC, characterized by enzymatic digestion, and tested for stability via temperature dependent gel electrophoresis and UV/Visible spectroscopy.