Netropsin Increases the Linking Number of DNA

The antibiotic netropsin (Fig. 1) from Streptomyces netropsis shows both antibacterial and antiviral activities (Zimmer 1975). This effect is thought to be a consequence of its high affinity for double-stranded DNA. Many studies have been performed on this interaction, not only because of its clinical importance, but also because examination of its structure shows that it may be a model for protein-nucleic acid interactions. A recent study (Votavova et al. 1981) shows that netropsin- and lysine-containing polypeptides do not, in fact, compete with each other for binding sites on DNA. A wide variety of physicochemical techniques have been used, including circular dichroism (Zimmer and Luck 1970; Luck et al. 1977), sedimentation velocity (Luck et al. 1974), viscosity (Zimmer et al. 1971; Reinert 1972; Luck et al. 1977; Reinert et al. 1979), UV spectroscopy (Zimmer et al. 1971), nuclear magnetic resonance (NMR) (Patel and Canuel 1977; Patel et al. 1981), thermal...