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Analysis of Rat Liver Chromatin and Nuclear Proteins after Nutritional Variation^1,2,

Department of Molecular Genetics, Wadley Institutes of Molecular Medicine, 9000 Harry Hines, Dallas, TX 75235

Chemical composition of liver chromatin was determined for rats fed a complete stock diet, or a diet lacking protein or fat. High carbohydrate, fat-free (diet 1) and low carbohydrate, protein-free (diet 2) diets were selected because they elicit structural alteration in chromatin as measured by incubation with micrococcal nuclease (E.C. 3.1.4.7). In the present study, either dietary treatment caused an increase in mass ratios of RNA:DNA and nonhistone:DNA, relative to control ratios. The nonhistone:DNA ratios in liver of rats fed diet 1 or diet 2 were 2.4-fold and 3.5-fold, respectively, larger than control ratios. The histone:DNA ratio remained relatively constant among all three dietary treatments. Liver nuclei were purified from rats fed each dietary treatment and were solubilized in 9 M urea. The nuclear proteins were analyzed by two-dimensional electrophoresis and visualized with a silver treatment that stains proteins in color. The electrophoretograms presented show preferentially proteins with low molecular weights and acidic pIs, two characteristics of nonhistones. The two-dimensional protein patterns are nearly identical for nuclear proteins from all three treatments. Analysis of the electrophoretograms indicates that the diet-induced increased nonhistone:DNA ratios are apparently not attributable to new species of protein, but rather to increased relative abundance of many proteins in the existing populations.

KEY WORDS: • nonhistone proteins • chromatin • protein restriction • fat restriction • two-dimensional electrophoresis

¹ Supported in part by the Oree Meadows Perryman Molecular Genetics Laboratory for Cancer Research grant from Meadows Foundation Inc., Dallas, TX, and by Department of Health and Human Services Grants 1 RO1 AM28 162-01 to CEC and 1 RO1 AM28252-01 to JSS.

² A portion of this paper was presented at the XII International Congress of Nutrition, San Diego, CA, August 16–21, 1981, abs. 610.

Manuscript received 23 November 1981.