Effect of distamycin a on the structure and template activity of DNA in RNA - polymerase system

Intranuclear incorporation of thymic low molecular weight RNA by murine bone marrow immunoblasts and inhibition of plasma cell formation by a derivative of rifampicin

An in vitro culture system for the proliferation of IgG-forming plasma cells from mouse bone marrow cultures has previously been described. The present study attempts to elucidate the mode of action of thymic RNA in these cultures. Autoradiography after using radiolabeled thymic RNA showed that radioactive material was mainly incorporated into the nuclei of IgG-forming plasma cells. No radiolabeled thymic RNA was incorporated into the cells except immunoblasts. The incorporated thymic RNA was acid insoluble and digested by RNase, but resistant to DNase and pronase. Radioactivity in the nucleotide pool after the cells were cultured with radiolabeled thymic RNA was negligible, indicating that reutilization of degraded RNA did not occur in the nuclei of the plasma cells. Moreover, the incorporation of radiolabeled thymic RNA by the cells was not prevented by excess unlabeled nucleosides. Escherichia coli transfer RNA, L-cell RNA and synthetic polynucleotide poly(A-U) were incorporated but were distributed in a different manner in the cells. A derivative of rifampicin, 2'5'-dimethyl N(4') benzyl-N(4')[desmethyl]rifampicin (AF/ABDMP), a possible inhibitor of RNA-dependent DNA polymerases, suppressed both the incorporation of thymic RNA and the differentiation of immunoblasts. AF/ABDMP suppressed DNA synthesis by bone marrow cultures to the same level as those pretreated with anti-mouse B-cell antibodies and complement. DNA dependent RNA polymerase activity was observed in the supernatant of bone marrow cultures stimulated by normal syngeneic thymic RNA and human gammaglobulin as antigen. These results imply a possible relationship between B-cell differentiation and RNA-dependent DNA polymerases.

Aspects of specific DNA-protein interaction; local bending of DNA molecules by in-register binding of the oligopeptide antibiotic distamycin

Distamycin A binds strongly/moderately to DNA below/above r = 0.08 molecules bound per DNA phosphate. Titration viscometric measurements for high and low molecular weight DNA yielded the relative changes of DNA persistence length, delta alpha/alpha 0, and contour length, delta L/L0 (Nucl. Acids Res. 7 (1979) 1375). delta L/L0 is negligible/positive in the range below/above r = 0.09 at 0.2 M Na+! A two-line covering of the small groove by ligand molecules explains the increase of contour length. The characteristic delta alpha/alpha 0 drop is quantitatively interpreted by local DNA bending (kinking). The underlying theoretical basis is presented in two appendices and applied, in a third one, to literature data for the DNA-actinomycin system. The angle gamma of local DNA bending as induced by complex formation with different distamycin derivatives is presented for DNA species of different base composition. By means of appropriate model, a length mismatch per dinucleotide of (0.03(2) +/- 0.01)nm [or (0.04(3) +/- 0.01)nm] was derived from the experimentally obtained bending angle per dinucleotide of (1.6 +/- 0.4)0 [or (2.1 +/- 0.05)0], independent of DNA base composition and distamycin chain length.

Protection of (dA.dT) cluster regions in the DNAase I cleavage of DNA by specific interaction with netropsin

The specific DNA binding ligand netropsin selectively blocks dA-dT base pairs in clusters containing two or more consecutive thymine residues at the dNAase I cleavage sites of DNA. Using CD and UV absorption measurements it is shown, that at various ratios of netropsin to nucleotide concentrations and even at satuation of ligand interaction the enzyme cuts along regions containing dG-dC pairs sandwiched between dA-dT pairs. This follows a slow kinetics and is associated with a release of netropsin from those segments. These facts suggests the usefulness of the partial protection of certain DNA sequences in DNAase I cleavage sites in producing DNA fragments in structural studies of the genome. A possible interpretation of the effect of netropsin binding on the enzymatic hydrolysis of phosphodiester bonds of the helix is discussed.

Thermal denaturation of distamycin A--DNA complexes as followed by hyperchromic spectra

Interaction of distamycin A with calf spleen DNA is investigated by the method of hyperchromic spectra. Hyperchromic spectra of complexes are partitioned into the components corresponding to the denaturation A . T and G . C base pairs and dissociation of the ligand, fractions of respective components are found as a function of temperature. A scheme of melting of successive regions of DNA with different G+C content together with the scheme of distamycin A redistribution in the course of thermal denaturation is presented.

Influence of cationic triphenylmethane dyes upon DNA polymerization and product hydrolysis by Escherichia coli polymerase I

The cationic triphenylmethane dyes crystal violet, methyl green, and malachite green inhibited DNA synthesis catalyzed by Escherichia coli B polymerase I (polymerase I). Lower concentrations of the dyes inhibited DNA replication as a direct function of the proportion of AT to GC in the DNA of Clostridium perfringens, Escherichia coli, and Micrococcus lysodeikticus. When the intercalant proflavin was employed, the GC-rich micrococcal DNA was most severely inhibited. In addition, both the triphenylmethanes and proflavin inhibited product hydrolysis catalyzed by polymerase I.

Effect of distamycin A on the primary and secondary immune response of mouse spleen cells in vitro against sheep erythrocytes

The effect of distamycin A (DMC) on the primary and secondary immune response of mouse spleen cells, cultured in vitro in the presence of sheep erythrocytes as an antigen, was studied. It was found that the primary response was extremely sensitive to DMC during the first 24 hrs of culture and then gradually became more and more resistant to the immunosuppressive effect of the drug. Right from the start of culture, however, the secondary response was much more resistant than the primary one to the inhibitory action of DMC. These results could not be reproduced by treating the cultures with inhibitors of DNA-dependent DNA synthesis (such as cytosine arabinoside) or inhibitors of DNA-DEPENDENT RNA synthesis (such as actinomycin D).

Congocidine and distamycin A, antipoxvirus antibiotics

The antibiotics congocidine and distamycin A inhibited the replication of Shope fibroma and vaccinia viruses in BSC(1) cells. Treatment of infected cultures with congocidine for a 12-hr period resulted in an irreversible inhibitory effect on virus development. A longer period of treatment with the antibiotic also resulted in inhibition of the residual infectious virions present in the treated cells. Distamycin A inhibited the replication of poxviruses, but its inhibitory effect was reversed when the antibiotic was removed from the infected cells even as long as 24 hr after treatment. The inhibitory effect of distamycin A and its reversibility resembled the antipoxvirus activity of rifampin.

Optical rotatory dispersion properties of nucleic acid complexes with the oligopeptide antibiotics distamycin A and netropsin

ORD measurements of nucleic acids in the presence of the oligopeptides netropsin and distamycin A have indicated association of the antibiotics with DNA and strong conformational changes of the DNA structure with specificity to AT-rich helical regions. The RNA conformation is relatively unaffected by these antibiotics. The results are explained in terms of a perturbation of the DNA secondary structure as well as of the chromophore system of the oligopeptides.