Sn. Khrapunov et al., MECHANISMS OF STABILIZING NUCLEOSOME STRUCTURE - STUDY OF DISSOCIATION OF HISTONE OCTAMER FROM DNA, Biochimica et biophysica acta, N. Gene structure and expression, 1351(1-2), 1997, pp. 213-222
The influence of ionic strength on DNA-histone and histone-histone int
eractions in reconstituted nucleosomes was studied by measuring the pa
rameters of histone tyrosine fluorescence: fluorescence intensity and
lambda(max) position. The first parameter is sensitive to histone-DNA
interactions. The changes of the second one accrue due to hydrogen bon
d formation/disruption between tyrosines in the histone H2A-H2B dimer
and the (H3-H4)(2) tetramer. The simultaneous measurement of these par
ameters permits the recording of both the dissociation of histone comp
lexes from DNA, as well as changes in histone-histone interactions. As
ionic strength is increased, the H2A-H2B histone dimer dissociated fi
rst, followed by dissociation of the (H3-H4)(2) tetramer [Yager, T.G.,
McMurray, C.T. and Van Holde, K.E. (1989) Biochemistry 28, 2271-2276]
. The H2A-H2B dimer is dissociated in two stages: first, the ionic bon
ds with DNA were disrupted, followed by the dissociation of the histon
e dimer from the tetramer. And secondly, the disruption of dimer-tetra
mer specific H-bonds. It was established that the energy of electrosta
tic interactions of the histone dimer with DNA within the nucleosome i
s much less than the energy of interaction of the histone dimer with t
he tetramer.