| Abstract: | The secondary structure of histones H2B and H3 from calf thymus has been quantitatively studied in heavy water solutions in a wide range of histone concentrations, pD, and concentrations of sodium chloride by an infrared spectroscopy method. Also, the interactions between molecules of different histones in equimolar mixtures H2A-H2B, H2A-H3, H2A-H4, H2B-H3, H2B-H4, H3-H4, and H2A-H2B-H3-H4 have been investigated using the same method. For H2B and H3 conditions favourable for aggregation have been shown to induce the formation of pleated sheet structure. When the pD and concentration of NaCl are in a physiological range, the secondary structure of H2B and H3 contains about 15% of alpha-helix, 4% of parallel pleated sheet structure, 14% of antipatallel pleated sheet structure in H2B and 18% in H3. For mixtures in all cases, except H2A-H4, there is an interaction between molecules of different histones followed by a reduction of the antiparallel pleated sheet structure content. The data on the secondary structure of histones in different states (under self-association, in mixtures, in nucleosomes, and in chromatin) have been discussed and it is suggested that: 1) the secondary structure of histones in chromatin is essentially similar to that in the state of self-association; 2) in the core nucleosome particle the quantity of DNA (in nucleotide pairs), and the quantities of alpha-helix and antiparallel pleated sheet structure (in peptide groups) satisfy the relation 1 : 1 : 1. |
