Naphthyridinomycin, a DNA-reactive antibiotic.

Naphthyridinomycin is a novel quinone antibiotic that is produced in liquid shake cultures by Streptomyces lusitanus. Fermentation studies have shown that this antibiotic is produced maximally after 96 h of cell growth. L-[methyl-3H]methionine efficiently labels naphthyridinomycin when it is added to a fermentation mixture 24 h before culture is harvested. Unlabeled and radioactively labeled naphthyridinomycin were used to determine the mechanism of action of this unique antibiotic. Naphthyridinomycin inhibited bacterial growth primarily by inhibiting DNA synthesis. The structural similarity between naphthyridinomycin and the saframycins suggested that naphthyridinomycin might inhibit DNA synthesis by binding to the template. In vitro studies with radiolabeled naphthyridinomycin indicated that this antibiotic does specifically bind to calf thymus DNA. The binding reaction was enhanced by adding sulfhydryl-containing compounds; dithiothreitol was the best activating agent. DNA-naphthyridinomycin complexes were a poor substrate for enzymes that catalyze DNA-directed DNA and RNA syntheses. These results showed that naphthyridinomycin is similar to the saframycins in its reactivity toward DNA and suggested that the mechanism by which naphthyridinomycin inhibits DNA synthesis is through its ability to bind specifically to the DNA template of the cell.