[Spatial organization of the histone dimer H2A-H2B in solutions of different ionic strengths]

The spatial organization of histone dimer H2A-H2B in a solution of 0.1-1.0 M NaCl is characterized by the inclusion of 38% of radicals in the composition of alpha-helical segments, fluorescence quantum yield of 0.085 +/- 0.003, long-wave shift of absorbtion (lambda max = = 278.4 +/- 0.5 nm) and fluorescence spectra (lambda max = 304.4 +/- 0.3 nm) as compared to respective spectra of free tyrosine. The changing of position lambda max of tyrosine fluorescence of histones during denaturation has been shown. The degree of alpha-helicity of histone dimer H2A-H2B, fluorescence quantum yield and the number of tyrosyls perturbed by ethylene glycol do not change within the range of 0.1-1.0 M NaCl pH 7.6. At the same time dimer denaturation takes place at greater urea concentrations as the ionic strength of the medium increases. The quenching of tyrosine fluorescence of histone dimer H2A-H2B was performed using ions I-, Cs+ and acrylamide. It has been shown that, at a concentration of NaCl 0.5 M, dimer compactization takes place, as well as the screening of some part of tyrosyls for the quenching effect of Cs+. Our experiments made it possible to identify three zones in the composition of histone dimer H2A-H2B and determine the number (ni) and fluorescence quantum yields (qi) of tyrosyls included in the following specific zones:zone I--n1 = 2, q1 = 0.136, zone II--n2 = 3, q2 = 0.08, zone III--n3 = 3, q3 = 0.055.