Nucleosomal repeat length in rat liver nuclei is decreased by a high carbohydrate, fat-free diet

Liver nuclei of Sprague-Dawley rats fed a high carbohydrate, fat-free diet (diet 1), a low carbohydrate, protein-free diet (diet 2), or a commercial stock diet were purified and mildly incubated with micrococcal nuclease (MN) (EC 3.1.4.7) until 5-6% of the chromatin was acid-soluble. Chromatin fragments generated by MN incubation were deproteinized and sized by electrophoresis. The mobilities of the DNA fragments were used to calculate by two independent methods nucleosomal repeat length. The nucleosome is the fundamental packaging unit of eucaryotic chromatin. When nuclei were incubated with MN for various lengths of time, the nucleosome repeat length for rats fed diet 1 was invariably shorter than that for stock diet-fed rats regardless of method of calculation. After incubation with MN for 10 minutes, the nucleosome repeat length of nuclei from rats fed diet 2 was virtually identical to that for stock diet-fed rats. In addition, after a 30-minute incubation, 32.4% of chromatin from nuclei of rats fed a lipogenic diet was of mononucleosome size, whereas only 9.9% and 20.6% was of the same size in nuclei of rats fed diet 2 or stock diet, respectively. These observations suggest that liver chromatin of rats fed a lipogenic diet may be in a different configuration than that from rats fed diet 2 or stock diet.