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The reaction was terminated and the histones, and most nonhistones, were removed by adding the nuclease-treated chromosomes to a solution containing dextran sulfate (2 mg/ml) (Pharmacia), heparin (0.2 mg/ml) (Sigma), 10 mM Tris (pH 9.0), 10 mM EDTA, 0.1% Nonidet P40, and 1 mM phenylmethylsulfonyl fluoride (PMSF) at a ratio of 1 volume of chromosomes to 3 volumes of solution.

What is the function of dextran sulfate and heparin in removing the proteins ?

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up vote 5 down vote accepted

See here.

Histones are basic proteins (cationic, high pI) because they are required to interact with polyanionic DNA at physiological pH. Heparin and dextran are polyanions which form insoluble salts with the cationic histones.(Dextran is a polymer of glucose. In dextran sulphate it is derivatised with sulphonate groups creating a polyanionic material.)

Immobilised heparin is sometimes used as an affinity matrix for purification of DNA-binding proteins like transcription factors.

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