[A synthetic zinc chelating peptide competes for DNA binding sites with antibiotics, adsorbed in a minor DNA groove].

Effects of sibiromicyn, distamicyn A and its analogs on binding to DNA and to poly(dA).poly(dT) are reported for a 23-amino acid synthetic zinc-binding peptide, a part of the DNA-binding domain of the transcriptional activator GAL-4. Circular dichroism and fluorometry have shown that the synthetic peptide and two distamicyn A analogs compete for binding sites on DNA and on poly(dA).poly(dT). Antibiotic sibiromycin which forms a covalent bond with a guanine 2-amino group in the minor DNA groove can displace the peptide from a 19 bp self-complementary oligonucleotide serving as a specific target site for Gal-4 protein. The peptide is shown to bind to a glucosylated phage T2 DNA, but its affinity to T2 DNA is weaker than to calf thymus DNA under the same conditions. A method to estimate binding constant and size of the binding site for the synthetic peptide and poly(dA).poly(dT) is proposed based on the binding isotherms of distamycin analogs in the absence and in the presence of the peptide. Using isotherms of binding to poly(dA).poly(dT) for two distamycin analogs with binding constants differing 60-fold, the binding constant of the peptide in the presence of 0.1 M NaCl is estimated as 1.4.10(7)-1.8.10(7) M-1.