Ca2+-Binding Proteins in Nuclei

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Abstract
Nuclei isolated from skeletal muscle of 15-day-old chick embryos, adult chickens, rabbits and from rat liver contain on the average 8–18 nmol Ca2+/mg protein. Digestion of nuclei with DNAase I and RNAase at 37 C for 8–12 h reduced the Ca2+ binding by more than 90%. After nuclease treatment, Ca2+-binding proteins were identified in the nonhistone chromosomal protein fractions and in the insoluble residue by equilibrium dialysis and centrifuge transport, in media of 0.1 M KCl and 1 mM MgCl2. The interaction of Ca2+-binding proteins with chromatin may be of importance in the regulation of the gene expression in response to changes in cytoplasmic and nucleoplasmic free-Ca2+ concentration.