DNA sequence selection by tightly-bound nonhistone chromosomal proteins

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Abstract
Extraction of chicken reticulocyte chromatin with 2.0 M NaCl removed 96% of chromosomal protein and yields two DNA components after dialysis and high-speed centrifugation. The bulk of chromosomal DNA (ca. 99%) is rendered free of protein, and is thus soluble in 10 mM Tris-HCl, pH 8.0. The other component (ca. 1%) displays a high protein/DNA ratio, and is insoluble in 10mM Tris-HCl, pH 8.0. These DNAs can be separated on the basis of their solubilities. Analysis of the reassociation kinetics with total chicken DNA of these DNAs reveals marked differences. Whereas total DNA and the soluble component (DNA-S) have rapidly reassociating components, the insoluble component (DNA-P) is devoid of these components, and is therefore composed completely of unique sequence DNA. Cot 1/2 values indicate that DNA-S is substantially depleted of some DNA-P sequences. We conclude that this segregation, as determined by tightly-bound nonhistone chromosomal proteins, selects a subset of total genomic DNA sequences, and suggests sequence-specific interaction between the tightly-bound nonhistones and DNA.