Conformational transitions of polynucleotides in the presence of rhodium complexes

T. J. Thomas, T. Thomas

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6 Scopus citations


We studied the effects of hexammine and tris(ethylene diamine) complexes of rhodium on the conformation of poly(dG-dC)·poly(dG-dC) and poly(dG-m5dC)·poly(dG-m5dC) using spectroscopic techniques and an enzyme immunoassay. Circular dichroism spectroscopic measurements showed that Rh(NH3)63+ provoked a B-DNA→Z-DNA→Ψ-DNA conformational transition in poly(dG-dC)·poly(dG-dC). Using the enzyme immunoassay technique with a monoclonal anti-Z-DNA antibody, we found that the left-handedness of the polynucleotide was maintained in the Ψ-DNA form. In addition, we compared the efficacy of Rh(NH3)63+ and Rh(en)33+ to provoke the Z-DNA conformation in poly(dG-dC)·poly(dG-dC) and poly(dG-m5dC)·poly(dG-m5dC). The concentrations of Rh(NH3)63+ and Rh(en)33+ at the midpoint B-DNA→Z-DNA transition of poly(dG-dC)·poly(dG-dC) were 48 ± 2 and 238 ± 2 μM, respectively. The Ψ-DNA form of poly(dG-dC)·poly(dG-dC) was stabilized at 500 μM Rh(NH3)63+. With poly(dG-m5dC)·poly(dG-m5dC), both counterions provoked the Z-DNA form at approximately 5 μM and stabilized the polynucleotide in this form up to 1000 μM concentration. These results show that trivalent complexes of Rh have a profound influence on the conformation of poly(dG-dC)·poly(dG-dC) and its methylated derivative. Furthermore, the Rh complexes are capable of maintaining the Z-DNA form at concentration ranges far higher than that of other trivalent complexes. Our results also demonstrate that the efficacy of trivalent inorganic complexes to induce the B-DNA to Z-DNa transition of poly(dG-dC)·poly(dG-dC) poly(dG-m5dC)·poly(dG-m5dC) is dependent on the nature of the ligand as well as the polynucleotide modification. Differences in charge density and hydration levels of counterions or base sequence- and counterion-dependent specific interactions between DNA and metal complexes might be possible mechanisms for the observed effects.

Original languageEnglish (US)
Pages (from-to)1221-1235
Number of pages15
JournalJournal of Biomolecular Structure and Dynamics
Issue number6
StatePublished - 1990

All Science Journal Classification (ASJC) codes

  • Structural Biology
  • Molecular Biology

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