Polymorphism in B-DNA: X-ray diffraction studies on Li-DNA fibres.

From X-ray diffraction studies it is generally believed that B-DNA has the structural parameters n = 10 and h = 3·4 Å. However, for the first time we report that polymorphism in the B-form can be observed in DNA fibres. This was achieved by the precise control of salt and humidity in fibres and by the application of the precession method of X-ray diffraction to DNA fibres. The significant result obtained is that n = 10 is not observed for crystalline fibre patterns. In fact, n = 10 and h = 3·4 Å are not found to occur simultaneously. Instead, a range of values, n = 9·6–10·0 and h = 3·35 Å–3·41 Å is observed.

Interaction of non-intercalative drugs with DNA: Distamycin analogues.

Distamycin and netropsin are two oligopeptides which bind to DNA in a nonintercalative manner. Analogues of distamycin have been synthesized and their binding with poly d(A-T) studied using ultraviolet absorption spectroscopy. Preliminary biological activity tests on a gram positive bacteria using these analogues have also been carried out.