Effects of a low-protein diet on chromosomal non-histone proteins in rat liver

Young male rats were fed a low-protein diet (3% casein) for ten days and then their nuclear proteins were compared with those of rats given a control diet (25% casein). The results showed that the total nuclear protein content of the liver was increased 1.4-fold by the low-protein diet. Chromatin was prepared from isolated nuclei and chromosomal proteins were fractionated into histone proteins and non-histone proteins, the latter being further fractionated into urea-soluble non-histone proteins and DNA-binding non-histone proteins. Measurement of the protein content of each fraction showed that the increase of total nuclear protein induced by the low-protein diet was due to an increase of urea-soluble non-histone proteins, without any change in the content of DNA-binding non-histone proteins. On two-dimensional gel electrophoresis, the patterns of urea-soluble non-histone proteins in the two groups were similar, but the amounts of some proteins with moleculars weights of approximately 30, 000 and isoelectric points of around 7, were decreased in rats given the low-protein diet. No specific increase in the amount of any particular urea-soluble non-histone protein was detected in these rats. The two-dimensional gel electrophoretic pattern of DNA-binding non-histone proteins was not affected by the low-protein diet. As many reports have suggested the importance of non-histone proteins in gene regulation, the change of non-histone proteins observed in this study suggests that a low-protein diet might affect gene regulation. Identification of these non-histone proteins will contribute to our understanding of nutrition at the molecular level.