| Popis: |
Sedimentation velocity techniques have been used to study the effect of the antibiotic drug netropsin (Nt) on the structural properties of different forms of closed circular DNA. Nt removes supercoils upon interaction with positively supercoiled DNA and introduces negative supercoils upon binding to relaxed DNA. Applying the classic assay of DNA unwinding by ethidium to complexes of negatively supercoiled DNA with Nt, we found that, compared with naked DNA, more ethidium is needed to convert the Nt-DNA complex into a superhelix-free form. From the shift in the critical ethidium/nucleotide binding ratio, a Nt-mediated decrease in the linking number difference and superhelix density (or increase in the number of superhelical turns) of negatively supercoiled DNA is calculated, synonymous with an increase in the linking number and a decrease in the helical repeat of the relaxed form. A significant influence of the presence of intrinsic bends in the DNA duplex on the magnitude of the drug-induced alterations in DNA supercoiling could not be detected. |
