Salt and base sequence specific changes in the chiroptical properties of DNA

Chiroptical properties of natural DNA molecules differing in base composition were studied in solutions with high concentrations of monovalent sodium and caesium salts. It was found that the properties were dependent on the DNA base sequence and nature of both cations and anions. A comparison with the behaviour of the synthetic molecules of DNA demonstrated that the salt-induced changes in the natural molecules of DNA could not be accounted for by the appearance of the left-handed Z conformation. On the other hand, the tendency of the alternating A--T sequence to assume the novel X--DNA conformation seems to play a role even in the conformational properties of natural DNA.