Isolation and properties of nonhistone chromosomal proteins from pea chromatin
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We have separated the nonhistone chromosomal proteins of pea chromatin from other chromosomal constituents and have studied some of the biological functions of these proteins. After dissociation of pea chromatin in 3m NaCl, 5m urea (pH 8) and subsequent removal of urea, the chromosomal proteins are separated from DNA on Bio-Gel A50. Histones are then separated from nonhistones by chromatography on Bio-Rex 70 in the presence of 0.35m NaCl and 5m urea. The resulting nonhistone proteins are concentrated on a DEAE-cellulose column.
No detectable histone remains in the nonhistone protein fraction. All of the nonhistone proteins are qualitatively but not quantitatively recovered. The major nonhistone proteins are acidic in amino acid composition, heterogeneous in molecular weight (10,000 to 68,000) and freely soluble at low ionic strength. The nonhistone proteins co-precipitate with histones at low ionic strength to form complexes. These can be redissolved in solutions of higher ionic strength. At physiological ionic strengths most nonhistone chromosomal proteins do not bind to histones. In reconstitution experiments, the mass ratio of nonhistone chromosomal protein to DNA is 0.17 at saturation binding. An input ratio, protein to DNA, of about 20 is required to give half-maximal binding.In vitro transcription byE. coli RNA polymerase is not significantly affected by the presence of nonhistone proteins, either with pea DNA or pea chromatin as template.
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