Parallel-stranded duplex DNA containing blocks of trans purine- purine and purine- pyrimidine base pairs

A 30 base pair parallel-stranded (ps) duplex ps-Li * L2 composed of two adjoined purine- purine and purine-pyrimidine sequence blocks has been char-acterized thermodynamically and spectroscopically. The 5"-terminal 15 residues in both strands ('left-half') consisted of the alternating d(GA)7G sequence that forms a ps homoduplex secondary structure stabilized by d(G G) and d(A A) base pairs. The 3'-terminal 15 positions of the sequence ('right-half') were combin-ations of A and T with complementary reverse Watson-Crick d(A T) base pairing between the two strands. The characteristics of the full length duplex were compared to those of the constituent left and right halves in order to determine the compatibility of the tw