Conformational changes in histone IV

Abstract

SynopsisConformational change of histone IV, induced by phosphate, have been investigated by observing the intrinsic fluorescence of tyrosine residues and circular dichroism (CD). There is a fast conformational change upon the addition of phosphate, followed by a slow process with time constants in the range of minutes to hours depending upon both the phosphate and histone concentrations. The CD results indicate a-helix formation in the fast process, and @-sheet formation in the slow one, although other secondary and tertiary structural changes also may occur. The histone concentration dependence of the fast process is consistent with dimerization. Divalent phosphate is about ten times more effective than monovalent phosphate in inducing conformational changes. All of the changes are reversible.of New York,

The Interaction of Histone IV with Nucleoside Triphosphates

“…We find appreciably smaller slow changes than occur upon the addition of small anions (1,2). At Ho = 4.4 MM we do see small amounts of slow change at nucleotide to histone ratios of 3.0 or higher.…”

“…The sample temperature was maintained at 22.0 d 0.50. The instrument and techniques used for measurement of the intrinsic fluorescence of histone IV have been described (1,2,7). Excitation was at 280 nm with vertically polarized light.…”

“…The anisotropy of this emission is a function of the rate of rotational diffusion of the tyrosine residues and will increase if the tyrosine environment becomes more rigid. We have reported (1,2) that salt-induced conformational changes in histone IV that led to marked increases in fluorescence anisotropy could be separated into fast and slow components. In 25 mM NaCl, or with ADP solutions, no time dependence at all was seen over the range observed.…”

“…The amount of slow change, when it occurs, is small compared to that induced by small anions (1,2). When small changes were observed, the anisotropy was extrapolated to zero time, as described (1,2), to obtain the data shown in Fig. 1.…”

“…We have reported (1,2) that anions induce conformational changes in histone IV. We now report that ATP, GTP, CTP, and TTP also induce conformational changes in histone IV, and furthermore that the nucleotides act at low concentrations, of the same order of magnitude as the histone concentrations themselves.…”