Interaction of Non‐histone Proteins with DNA and Chromatin from Drosophila and Mouse Cells

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Abstract
The specificity of the binding of purified nonhistone proteins to DNA was investigated through 2 types of experiments. Using a nitrocellulose filter assay at a low protein/DNA ratio, the binding of mouse nonhistone proteins to mouse DNA was twice as great as the binding of mouse nonhistone protein to Drosophila DNA. The reverse experiment using Drosophila nonhistone protein confirmed that some protein/DNA complexes were specific. Protein/DNA complexes isolated by gel filtration chromatography indicated that 20 or 10% of the nonhistone protein was bound to homologous or heterologous DNA, respectively. Purified nonhistone proteins bound with lower efficiency (15%) than unpurified but with higher specificity to soluble chromatin than to naked DNA. This binding did not result from an exchange between chromatin nonhistone proteins and purified nonhistone proteins added in excess. DNA-bound and chromatin-bound proteins were analyzed on polyacrylamide gels. Whereas no major qualitative differences were observed with DNA-bound proteins, some proteins bound to homologous mouse chromatin were different from those bound to heterologous Drosophila chromatin. A possible role of DNA-bound nonhistone proteins in the regulation of gene expression is suggested.