Search

Purified non-histone proteins from mouse mammary cells bind specifically to homologous DNA or chromatin. Complexes of non-histone protein with DNA or chromatin, isolated on agarose columns, were transcribed with both Escherichia coli RNA polymerase and RNA polymerase B from calf thymus. The fact that complexing of DNA with non-histone proteins increases transcription by E. coli RNA polymerase but not by RNA polymerase B suggests different mechanisms of transcription by these two enzymes. Similar experiments with mouse and Drosophila chromatin indicate that non-histone proteins specifically stimulate the transcription of mouse chromatin by RNA polymerase B. Non-histone proteins stimulate the transcription of mouse mammary tumor virus sequences in chromatin by RNA polymerase B but not by E. coli RNA polymerase. We conclude that those non-histone proteins bound specifically to chromatin are able to activate the transcription of specific genes by eukaryotic RNA polymerase. [ABSTRACT FROM AUTHOR]

The specificity of the binding of purified non-histone proteins to DNA has been investigated through two types of experiments. Using a nitrocellulose filter assay at a low protein/DNA ratio, the binding of mouse non-histone proteins to mouse DNA was twice as great as the binding of mouse non histone protein to Drosophila DNA. The reverse experiment using Drosophila non-histone protein confirmed the interpretation that some protein · DNA complexes were specific. Protein · DNA complexes isolated by gel filtration chromatography indicated that 20% or 10% of the non-histone protein was bound to homologous or heterologous DNA respectively. Purified non-histone 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 non-histone proteins and purified non-histone proteins added in excess. DNA-bound and chromatin-bound proteins were analysed 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. These results suggest a possible role of DNA-bound non-histone proteins in the regulation of gene expression. [ABSTRACT FROM AUTHOR]