Fluorescence Studies on Chromatin Structure*

Internal architecture of the core nucleosome: fluorescence energy transfer studies at methionine-84 of histone H4

“…Our quenching accessibility and fluorescence emission intensity results (Chung & Lewis, 1985) are consistent with a less compact structure than that at 10 mM. A similar transition has been reported by many others using a wide range of physical and chemical cross-linking methods (Gordon et al, 1978;Martinson et al, 1979;Burch & Martinson, 1980Cantor et al, 1981;Libertini & Small, 1982;Schlessinger et al, 1982;Uberbacher et al, 1983). Neutron scattering experiments (Uberbacher et al, 1983) indicate that the principal changes in this transition involve partial unwinding of the encircling DNA supercoil and that the overall shape of the protein core changes little if at all.…”

“…Cys-110 of histone H3 is in very close proximity to its twin in a nucleosome and can interact across the dyad axis (Zama et al, 1977;Camerini-Otero & Felsenfeld, 1977;Lewis & Chiu, 1980;Cantor et al, 1981). On the basis of pyrene excimer fluorescence, we have recently identified a similar homotypic interaction involving the unique Met-84 residue of histone H4 (Chung & Lewis, 1986).…”

“…Fluorescence Energy Transfer. Ionic strength induced structural transitions in nucleosomes are accompanied by an increase in the distance separating the H3-H3 (Zama et al, 1977;Cantor et al, 1981) and H4-H4 (Chung & Lewis, 1986) contact sites within the histone octamer. The H3 studies used pyrene excimer fluorescence and singlet-singlet energy transfer methods which allowed the estimation of distances between two fluors.…”

“…Cantor and co-workers report that beyond 10 mM NaCl Cys-110 H3 fluor separation occurs only at ionic strengths greater than 500 mM NaCl and reaches a final value in excess of 7 nm (Cantor et al, 1981). However, the environment polarity and accessibility to quenching agents of fluors attached at Cys-110 H3 increases significantly in the range 100-300 mM (Cantor et al, 1981). Thus, the H4 changes appear to precede those for H3.…”

“…This model would account for the increased fluor separation while preserving the overall shape (Ausio et al, 1984; Yager & van Holde, 1984) and secondary structure of its constituents (Thomas et al, 1977;Savoie et al, 1985). Cantor and co-workers report that beyond 10 mM NaCl Cys-110 H3 fluor separation occurs only at ionic strengths greater than 500 mM NaCl and reaches a final value in excess of 7 nm (Cantor et al, 1981). However, the environment polarity and accessibility to quenching agents of fluors attached at Cys-110 H3 increases significantly in the range 100-300 mM (Cantor et al, 1981).…”