title: DNA torsional dynamics by multifrequency phase fluorometry.
abstract: The time decay of the fluorescence polarization anisotropy of calf thymus DNA-ethidium complexes is obtained from measurements with sine-modulated excitation employing the so-called multifrequency phase fluorometry. A torsional dynamics model developed by J. M. Schurr [(1984) Chemical Physics, Vol. 84, pp. 71-96] and translated into the frequency domain is found here to describe accurately DNA-ethidium fluorescence data collected under modulated excitation. At a low dye/DNA ratio (1:400) the value of the DNA torsional constant (alpha = 4.63 +/- 0.2 10(-12) dyne cm) fitting the data agrees very well with the known values of alpha. When the measurements are extended to a higher ethidium/DNA ratio, energy transfer effects between intercalated dyes are observed. A theoretical prediction of the donor and acceptor dye contributions to the fluorescence polarization anisotropy is made here, taking into account also dye-dye distance distributions.
authors.affiliation: Dipartimento di Fisica, Universitá degli Studi di Milano, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Collini
authors.forename: G
authors.initials: G
authors.lastname: Chirico
authors.forename: G
authors.initials: G
authors.lastname: Baldini
mesh_terms: D000818:Animals; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D005470:Fluorometry / Q000379:methods; D013816:Thermodynamics
chemical_list: D004247:DNA