Characterization of a DNA binding protein from rat liver chromatin which decreases during growth

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Abstract
A nuclear nonhistone protein which decreases in chromatin during growth was isolated in high purity from the chromatin of normal rat liver nuclei by gel electrophoresis and column chromatography. This protein, designated BA, has a MW of 31,000, an acidic to basic amino acid composition ratio of 0.9, and contains 1 tryptophan residue per molecule. Hydrazinolysis indicated protein BA has a lysine carboxyl terminus; the amino terminal is blocked as no reaction occurred with dansyl chloride. Maps of tryptic peptides of protein BA contained 46 spots. Protein BA binding to various DNA was examined by the nitrocellulose filter assay. Binding was slightly enhanced by 2 mM Mn2+; Mg2+ decreased binding. Binding was optimal at neutral pH and an ionic strength of 0.2 M NaCl. Equilibrium competition binding studies indicated a binding preference of protein BA for dA-dT rich DNA.