TERTIARY STRUCTURE MOTIF OF OXYTRICHA TELOMERE DNA

The tertiary structure of a single-stranded DNA containing the sequenc e of Oxytricha telomere DNA has been determined. This DNA adopts a com pact tertiary structure that consists of four base-paired tetrads of g uanine residues which are connected by three loops. The tetrads show s ignificant deviations from planarity, and two of the loops exhibit sig nificant loop-loop interactions. The structure of this telomere contai ns syn-thymine residues, which are in the loops, as well as an intralo op pyrimidine-pyrimidine base pair between residues that are separated by a single residue. The tertiary structure of the telomere DNA is co nsistent with prior results that showed that two thymines distant in s equence could be photo-crosslinked. The overall folding pattern of thi s telomere DNA is similar to that previously determined for a DNA apta mer, which binds to and inhibits thrombin, though the details of the t wo structures are quite distinct.