Differential DNase I sensitivity of the albumin and alpha-fetoprotein genes in chromatin from rat tissues and cell lines.

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We have examined the DNase I sensitivity of the albumin and alpha-fetoprotein (AFP) genes in different rat tissues (adult liver and kidney) and cloned cell lines (hepatoma 7777-C8, JF1 fibroblasts), which show drastic differences in the level of expression of these two genes. This was done by studying the disappearance of defined restriction endonuclease fragments of these genes as a function of limited DNase I digestion. The sensitivity of these genes was compared to that of a gene not expressed in the hepatic cells and to that of a ubiquitously expressed gene. In nuclei from adult rat liver the albumin and AFP genes were preferentially degraded by the nucleolytic action of DNase I, whereas they were not in rat kidney nuclei. In the hepatoma cells the AFP gene was much more sensitive to DNase I digestion than the albumin gene; both genes were very resistant to DNase I action in fibroblastic nuclei. When analyzed in relation to the level of gene expression our results indicate that alterations in the chromatin structure of the albumin and AFP genes might be involved in the early establishment of the tissue-specific potential of overt gene expression; such alterations reflected in an altered DNase I sensitivity do not appear to be responsible for the changes in gene activity occurring during the terminal differentiation of the hepatocyte; and modifications in the chromatin structure of these genes might occur during oncogenic events; these structural modifications could be related to the changes in gene expression observed in hepatocarcinogenic processes.

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