Nine DNA sequences related to the purine strand of the human centromeric satellite (AATGG)n·(CCAAT)n repeat have been studied by two-dimensional nuclear magnetic resonance spectroscopy. Earlier studies have suggested that the structure of (AATGG)n sequence has an equilibrium between the duplex form and a fold-back form. Structural refinement of d(CAATGG) and its related sequences by an NOE-constrained simulated annealing procedure reveals that the duplex form incorporates dynamic type-I G-A base pairs. 1D exchangeable proton NMR data support this model. The reverse sequence motif (GGTAA) destabilizes the structure.
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