The use of fluorescence anisotropy decay of poly d(A-T) ethidium bromide complex to estimate the unwinding angle of the double helix.
We measured the fluorescence decay under polarized light, of ethidium bromide bound to the poly d(A-T) isolated from Cancer Pagurus. The decay of the whole fluorescence is a single exponential function revealing a good homogeneity of the binding sites. The anisotropy decay due to energy transfers between the ethidium bromide molecules bound to a same poly d(A-T) molecule has been analysed, with a Monte Carlo calculation. We found the dye unwinds the poly d(A-T) duplex by an angle of 17 degrees plus or minus 2 degrees. This result is in agreement with the value previously found in the case of calf thymus DNA-ethidium bromide complex, although the base compositions of the two nucleic acids are different.
D000227:Adenine Nucleotides; D001665:Binding Sites; D003854:Deoxyribonucleotides; D004996:Ethidium; D008433:Mathematics; D008722:Methods; D009690:Nucleic Acid Conformation; D011119:Polynucleotides; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics; D013942:Thymine Nucleotides
D000227:Adenine Nucleotides; D003854:Deoxyribonucleotides; D011119:Polynucleotides; D013942:Thymine Nucleotides; D004996:Ethidium