Gene Masking in Cell Differentiation: The Role of Non-Histone Chromosomal Proteins

Abstract

Evidence that the proteins associated with DNA in chromatin might perform a regulatory role in transcription first emerged in some studies in the early 1960’s in which the efficiencies of DNA and nucleoprotein as templates for the synthesis of RNA by bacterial RNA polymerase were compared. In all these experiments it was found that DNA was a much less efficient template when it was present as nucleoprotein than when it was free. These early experiments were seriously criticised because of the limited solubility of nucleoprotein in the buffer solutions used in the assays. To obviate this objection, Paul and Gilmour [1] isolated RNAs transcribed from the different templates and compared these by hybridisation back to DNA. These studies showed clear-cut differences between the RNA derived from DNA and RNA derived from nucleoprotein; they indicated that a restricted subset of sequences in DNA was transcribed in nucleoprotein. Moreover, it was demonstrated that the RNAs transcribed from chromatins from different tissues behaved differently and, in competition experiments, tended to resemble the natural RNAs isolated from nuclei from the tissues from which the chromatin preparations were made.