The effects of mechanical tension and the steffimycin antibiotics on D.N.A. conformation

Abstract

The conditions necessary to produce stable specimens of D.N.A. under mechanical tension were investigated. This involved the examination of the sodium chloride content of D.N.A. fibres and a study of the relative humidity range within which the stretched form is maintained.
X-ray and optical methods were used to obtain helical parameters with sufficient resolution to construct a series of models of the structure. These models were built so that the destructive interference of scattered X-rays would result in calculated intensity data which closely resembles the observed diffracted intensities.
The resulting models present various advantages in the replicative and transcriptional roles of the molecules.
Steffimycin and steffimycin B are two antibiotics which bind to nucleic acids and an investigation was carried out on the conformation of the resulting complex when formed with natural and synthetic D.N.A.'s, Spectroscopic studies were made to examine the extent of drug binding to D.N.A. and any base pair specificity of the interaction.
X-ray diffraction methods revealed that the helix pitch is extended in such a complex with the results best explained as the effect of intercalation of the drug chromophore between base pairs.
Model building studies of the D.N.A.-steffimycin conformation were carried out and a comparison of the mode and strength of binding of the two steffimycins and some other antibiotics was made.