Interaction of synthetic analogs of distamycin with DNA. Role of the conjugated N-methylpyrrole system in specificity of binding

Interaction of two synthetic analogs of distamycin (Dst), PPA and PAP, containing a saturated beta-alanine moiety replacing one N-methylpyrrole ring, with different polynucleotides and natural DNAs were studied using UV and CD spectroscopy. The results indicate that, similar to Dst, these analogs bind to DNA via the minor groove with a specificity towards AT-base pairs. It may be proposed that pyrrole chromophores in Dst probably do not play a role in the AT-base selectivity exhibited by Dst.     

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.     

Arrowroot (Marantha arundinacea) starch as a new low-cost substrate for alkaline protease production

The feasibility of arrowroot (Marantha arundinacea) starch for alkaline protease production using an alkalophilic Bacillus lentus isolate was evaluated in batch fermentations in shake flasks and in a bioreactor under a range of conditions. A new arrowroot starch-casein medium (pH 10.2) was formulated having a composition (%, w/v): arrowroot starch 1, casein 1, sodium succinate 0.25, NH₄Cl 0.05, NaCl 0.05, KH₂PO₄ 0.04, K₂HPO₄ 0.03, MgCl₂ 0.01, yeast extract 0.01 and Na₂CO₃ 1.05. The isolate produced a maximum protease yield (6754.7 U ml^–1) in this medium when grown for 72 h at 250 rev/min and 37 °C. Scaling-up studies in a bioreactor showed a 5-fold increase in alkaline protease yields (31899 U ml^–1) at a lower production time of 45 h, aeration of 1 v/v/m and agitation of 400 rev/min at 37 °C.     

Fibre diffraction of lithium DNA shows structural variability and deviation from a regular helical structure for the B-form

Recently, reports have appeared which show structural variations in B-DNA and indicate deviations from a uniform helical structure. We report for the first time that these indications are also present in the B-form fibre diffraction patterns for the lithium salt of natural DNA. We have used an improved method of controlling the salt concentration in the fibres. Our results are based on the appearance and disappearance of meridional reflections on different layer lines depending upon the salt.     

A detailed study of Li-DNA fibres at various salt concentrations reveals a non-helical B-DNA and a possible similarity of solution and solid state structures

A thorough investigation of salt concentration dependence of lithium DNA fibres is made using X-ray diffraction. While for low salt the C-form pattern is obtained, crystalline B-type diffraction patterns result on increasing the salt concentration. The salt content in the gel (from which fibres are drawn) is estimated by equilibrium dialysis using the Donnan equilibrium principle. The salt range giving the best crystalline B pattern is determined. It is found that in this range meridional reflections occur on the fourth and sixth layer lines. In addition, the tenth layer meridian is absent at a particular salt concentration. These results strongly suggest the presence of non-helical features in the DNA molecule. Preliminary analysis of the diffraction patterns indicates a structural variability within the B-form itself. Further, the possibility of the structural parameters of DNA being similar in solid state and in solution is discussed.