Distamycin-stabilized antiparallel-parallel combination (APC) DNA.

The formation of Antiparallel-Parallel-Combination (APC) DNA, a liner duplex with a segment of parallel-stranded (ps) helix flanked by conventional B-DNA, was tested with a number of synthetic oligonucleotides. The groove-binding ligand distamycin A (DstA) was used to stabilize the ps segment comprising five A x T base pairs. Two drug molecules bound per APC, one in each of the two equivalent grooves characteristic of ps-DNA.