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We report studies of the interaction of four anthracycline antibiotics, iremycin (IM), daunomycin (DM), aclacinomycin A (AM), and violamycin B1 (VM), with naked DNA, nucleosomal core particles, and 175 base pair (bp) nucleosomes lacking histone H1. In all cases the binding strength increases in the order IM less than DM approximately AM less than VM. The binding substrates increased in affinity for the drugs in the following order: core particles less than 175-bp nucleosomes less than DNA. The apparent DNA length increment per drug bound decreases in the progression IM greater than DM greater than AM greater than VM, the same serial order as is characterized by increasing binding affinity. Dichroism amplitude measurements show that for all drugs the long-wavelength absorbance transition moment is tilted by 26-29 degrees relative to the plane perpendicular to the helix axis; this angle probably corresponds to the long axis tilt of the intercalated chromophore. Finally, it was found that the ability of the drugs to inhibit DNA synthesis by Escherichia coli DNA polymerase I increases in the same order as their binding affinity.

The inhibitory effect of the polypeptide antibiotics netropsin and distamycin A on DNA dependent nucleic acid synthesis has been shown to be related to the base composition of the template DNA. A number of natural DNA's of quite different dA-dT content as well as poly (dI-dC)-poly (dI-dC), poly (dA-dT)-poly (dA-dT), poly (dA) - poly (dT) and poly (dG) - poly (dC) has been studied as templates in DNA and in part in RNA polymerase reaction. The highest binding efficiency of netropsin existing for (dA-dT) - containing DNA polymers and the less pronounced interaction with the (dI-dC)-containing polymer shown by the melting and CD spectrral behaviour of the complexes are entirely reflected in the template inactivation. The same is evident for distamycin A. However, in contrast to netropsin the antibiotic distamycin A exhibits some binding tendency to poly (dG) - poly (dC). Binding effects of a netropsin derivative to DNA and (dA-dT) -containing polymers suggest the importance of hydrogen bonds of the peptide groups in the complex formation.

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Resistomycin preferentially inhibits RNA synthesis in comparison to DNA and protein synthesis in intact bacterial cells. Studies with cell-free systems have shown that the antibiotic interferes with DNA and RNA synthesis, while protein synthesis is inhibited to a much lesser extent. Detailed studies in cell-free systems indicate an interaction of resistomycin with DNA- and RNA polymerase. In the case of RNA polymerase this was proved by CD measurements, whereas no interaction of the antibiotic with DNA, RNA, and homopolynucleotides could be found. One can conclude that the binding of the antibiotic to RNA polymerase is the basis for its interference with RNA synthesis.

Resistomycin preferentially inhibits RNA synthesis in comparison to DNA and protein synthesis in intact bacterial cells. Studies with cell-free systems have shown that the antibiotic interferes with DNA and RNA synthesis, while protein synthesis is inhibited to a much lesser extent. Detailed studies in cell-free systems indicate an interaction of resistomycin with DNA-and RNA polymerase. In the case of RNA polymerase this was proved by CD measurements, whereas no interaction of the antibiotic with DNA, RNA, and homopolynucleotides could be found. One can conclude that the binding of the antibiotic to RNA polymerase is the basis for its interference with RNA synthesis.As described earlier (BRADLER and ECKARDT 1972), two antibiotics were isolated from fermentations of Xtreptomyces griseoflavus JA 3733. One of them was shown to be identical with resistomycin which was first isolated by BROCKMANN and SCHMIDT-KASTNER (1954). Resistomycin is an antibacterial and antiprotozoal antibiotic with only very low solubility in water. The chemical structure of resistomycin is shown in This paper describes the action of the drug on intact bacterial cells and its effects on cell-free DNA, RNA, and protein syntheses to localize more precisely the point of attack. Furthermore, the binding ability of the antibiotic to DNA, RNA, protein, and homopolynucleotides was studied by means of spectrophotometric and circular dichroism (CD) measurements and the results have been compared with those obtained by in vivo and in vitro experiments. Materials and methodsFor preparation of resistomycin solutions 1.9 mg of the antibiotic were dissolved in 0.2 ml of 0.1 N NaOH and diluted with water. The antibiotic solution was prepared immediately before use.Synthesis of cellular macromolecules: Bacillus subtilis 168 thy-ind-was grown in glucose-salt medium as previously described (HAUPT and ECKARDT 1972).