Year: 1982
Type: article
Abstract: Binding of the frameshift mutagen ethidiuin broin.ide to eight dinucleoside phosphates of different complementary base sequences, to trinucleoside diphosphates with mismatched bases capable of forming bulged structures (CpUpG and GpUpG + CpC), and to calf thynius DNA at different counterion concentrations was studied by optical methods, notably UV-visible spectroscopy, circular dichroism (CD), and fluorescence detected circular dichroisna (FDCD).The ethidium ion intercalated between the base pairs of the minihelix formed by the complementary dimers, and displaced the mismatched bases to form bulged structures with the trimers.The stoichiometry of the complexes was 2:1 oligonucleotide:dye (or 1:1:1 for non-self-complementary species).Equilibrium constants for complex formation showed a general preference for dye binding to complementary sequences in the order: Py(3'-5')Pu > Pu(3'-5')Pu Py(3 1 -5')Py > Pu(3'-5')Py where Py a pyrimidine base and Pu a purine base.Complexes.with ribodinucleoside.phosphates had larger formation constants than their deoxyriboanalogs.Above 300 tim, where only the dye absorbs light, the induced CD spectra of the complexes had bands at 510, 375, 330, and 307 tim, with the magnitude of the 307 tim band, per bound dye, being the largest and sequence dependent.The CD spectra down to 220 tim of some complexes were obtained by FDCD measurements; between 220 and 300 tim both the positions and the magnitudes of the bands were sequence dependent.At very low ionic strength, complexes of calf thymus DNA plus ethidium ion in different salt concentrations showed that the 307 tim CD magnitude increased with decreasing counterion concentration.Implications of the results for theories of the induced CD spectrum of the ethidium ion are discussed.
Source: Biochemistry
DOI: 10.1021/bi00540a024
Authors: Kenneth S. Dahl, Arthur Pardi, Ignacio Tinoco
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
Awards: G1702950523, G660437508, G7531008850
OpenAlex ID: W2119935041