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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.

We demonstrate by messenger RNA (mRNA) . complementary DNA (cDNA) hybridization that nutrient variation can alter 1) the frequency in which entire classes or families of liver polyadenylated mRNAs [poly(A)+ mRNAs] are present within the cell and 2) the sequence complexity of those transcripts. Feeding a carbohydrate-rich, fat-free diet to rats for 5 days resulted in an increased sequence complexity of rare and moderately abundant liver poly(A)+ mRNAs when compared with poly(A)+ mRNA from rats fed high fat or basal diets. In addition, the frequency of reiteration of abundant sequences increased approximately 10 times compared with the abundant poly(A)+ mRNAs of rats fed high fat or basal diet. The results indicate that the functionality of the template is influenced by nutrient concentrations and may be one means by which complex organisms achieve homeostasis.

The higher order structure of rat liver chromatin from nuclei of animals fed stock or semi-synthetic diets for 5 days was investigated by a specific enzymatic probe, micrococcal nuclease (EC 3.1.4.7). Micrococcal nuclease digests 50% of DNA in eukaryotic chromatin into acid-soluble nucleotides while 50% of the DNA is resistant to digestion because of associated nucleoproteins. This selective digestion of DNA reflects higher orders of structure of the universal chromatin subunit, the nucleosome, found in lower eukaryotes, plants and animals. When rats were fed a commercial stock diet, 50.3% of the DNA in liver chromatin was digested by micrococcal nuclease. However, when rats were fed various semi-synthetic diets, the amount of DNA susceptible to micrococcal nuclease digestion varied as a function of diet (P less than 0.0001). Differences in the amount of DNA susceptible to micrococcal nuclease ranged from 71.4% for chromatin of rats fed a high carbohydrate/fat-free diet to 38.8% for chromatin of those fed a low carbohydrate/protein-free diet. DNA fragments generated by brief micrococcal nuclease digestion were analyzed by electrophoresis on 2.5% polyacrylamide--0.5% agarose gels. Chromatin from rats fed the high carbohydrate/fat-free diet was more rapidly digested to the monomer nucleosomin-free diet. To our knowledge, these diet-induced alterations in the higher order structure of chromatin are the first to be reported as occurring by in vivo modulation.

Dot hybridization of messenger RNA (mRNA) and complementary DNA (cDNA) has been used to measure the relative levels of albumin and alpha-fetoprotein mRNA in liver of rats fed for 5 d a fat-free (carbohydrate-rich) diet, a high fat diet or a basal diet, all three of which were isonitrogenous. The level of albumin mRNA in rats fed the fat-free (carbohydrate-rich) diet was 30 to 45% of the level in animals fed the basal 4% fat diet. The concentration of another mRNA, that for alpha-fetoprotein, remained unchanged. It has been established by others that albumin mRNA levels and albumin synthesis are diminished in response to low levels of dietary protein. We show that albumin mRNA levels are lower than those observed in animals fed the basal 4% fat diet, even when dietary protein is adequate (30% wt/wt), if the nonprotein calories are derived solely from carbohydrate.