Interaction of calf thymus non-histone chromosomal protein HMG2 with H1,H5-depleted nucleosomes from chicken erythrocytes was studied by means of thermal denaturation and an N-(3-pyrene)maleimide fluorescence probe. Under low ionic conditions (2 mM Tris buffer plus EDTA) addition of 1-2 molecules of HMG2 per nucleosome markedly stabilized the segment of the linker DNA against thermal denaturation. Under approximately physiological ionic conditions (0.1 M NaCl) addition of two HMG2 molecules per nucleosome, labeled by N-(3-pyrene)maleimide at the sulfhydryl groups of Cys-110 of histones H3, resulted in a decrease of the pyrene excimer fluorescence corresponding to the slight movement of the sulfhydryl groups of the two histone H3 molecules apart.

Institute of Biophysics Czechoslovak Academy of Sciences Brno

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DNA looping by the HMG-box domains of HMG1 and modulation of DNA binding by the acidic C-terminal domain