Alteration of higher order structure of rat liver chromatin by dietary composition

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.