Influence of netropsin and distamycin A on the secondary structure and template activity of DNA.

Abstract

The action of netropsin and distamycin A on the DNA secondary structure and on the template properties of DNA in the DNA-and RNA-polymerase systems have been studied. Ultraviolet absorption measurements indicate characteristic hypochromic effects for the DNA-antibiotic complexes due to binding of netropsin and distamycin A to DNA. These are accompanied by the appearance of an absorption peak beyond 320 nm. This ultraviolet absorption maximum depends on the (A+T) content of DNA and disappears upon heat denaturation. These results together with earlier observations indicate an A and T specificity of the binding of the oligopeptides netropsin and distamycin A. As demonstrated by absorbance-temperature measurements netropsin increases considerably the thermal stability of DNA. Drastic changes can even be obtained with ratios below 5 moles netropsin per 100 DNA phosphate groups. The antibiotic dependent increase in the melting temperature is more pronounced for the DNA · netropsin than for the DNA · distamycin A complex. The structure of denatured DNA is also affected markedly by both antibiotics. From the results it is concluded that binding of netropsin and distamycin A to DNA is the result of their affinity to double-helical and base stacked regions. Comparison of the effect of these antibiotics on DNA-and RNA-synthesis in vitro shows that both netropsin and distamycin A inhibit the DNA- and RNA-polymerase reactions. In both systems the template activity of native as well as of denatured DNA is affected by these antibiotics. Using chromatin of Ehrlich ascites tumor cells as template it could be shown, that the nucleoprotein complex is as sensitive to the action of distamycin A as pure DNA.