Biochemical and physiochemical characterization of chromatin fractions with different degrees of solubility isolated from chicken erythrocyte nuclei.

Chicken erythrocyte chromatin was prepared according to two different methods [Fulmer, A. W., & Bloomfield, V. A. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 5968-5972; Ausio, J., Borochov, N., Seger, D., & Eisenberg, H. (1984) J. Mol. Biol. 177, 373-398] to give three main common fractions, according to its solubility (S) or insolubility (I) in 0.15 M NaCl buffers or to its further solubility in 0.25 mM ethylenediaminetetraacetic acid (E). From the biochemical point of view, all of them have been found to be undistinguishable. Analytical ultracentrifugation shows that all of these fractions can reversibly undergo the transition from the low to the higher order structure, through a nearly identical way of folding. Thermal denaturation profiles yielded three transitions having the same Tm's for the three fractions. The percentage of DNA melting in the first transition decreased in the order S greater than I greater than E, and the amount in the second transition increased in the same order. Together with the different solubility of these fractions in the presence of divalent ions, these results indicate that in the three fractions of chromatin studied, the amount of linker DNA bound to the nucleosome varied.