Low molecular weight peptidic fraction in the chromatin from normal and cancer cells: Control of transcription

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Abstract
DNA isolated from cell nuclei by intensive deproteinization with chloroform/isoamyl alcohol and phenol extractions contains a low molecular weight peptidic fraction in a quantity of about 20 μg/mg DNA. These peptides were characterized by chromatography on CM-Sephadex, Sephadex G-25, high performance liquid chromatography on μBondapak C18 and amino acid composition. The peptides control transcription in a reconstituted cell-free system with prokaryotic and eukaryotic RNA polymerase and stabilize the structure of double stranded DNA, while increasing its melting point. Their level is markedly decreased (by about 40%) in DNA prepared from tumor cells as compared to normal cell DNA. Transcriptional studies showed only a slightly increased template activity of DNA extracted at pH 9.5 versus DNA extracted at pH 6.0 for DNA preparations from tumor cells. However, there was a marked increase in template activity for DNA preparations treated at pH 9.5 from normal cells-232%, 124%, 97% and 78% for rat liver, mouse liver, mouse thymus and fibroblast L-929 cells, respectively. Also there was no difference in the melting point between these two preparations of DNA from tumor cells; normal cell DNA preparations showed increased melting point of preparations treated at pH 6.5. The data obtained indicate that the loss of low molecular weight peptides from tumor DNA during carcinogenesis is responsible for uncontrolled gene expression observed in cancer.