Mitochondrial DNA, RNA and protein synthesis in normal and hypothyroid developing rat liver

Mitochondrial DNA, RNA and protein synthesis in normal and hypothyroid rat liver between the ages of -3 and 21 days were followed. In normal rats DNA polymerase activity and protein synthesis behaved similarly, showing two peaks of activity, one at -3 and the other at 21 days of age. RNA polymerase activity did not change between days -3 and 14, whereas it increased by 21 days of age. Hypothyroidism delayed the developmental pattern of DNA polymerase activity, affected RNA polymerase activity only at 21 days, whereas it inhibited protein synthesis at birth and in the third week of life. The cytochrome aa3 content appeared to be affected by hypothyroidism at birth and at 21 days of age.     

Diurnal variations in endogenous RNA polymerase activity and amounts of nuclear non-histone protein,DNA and cytoplasmic protein in rat liver

Summary From rats fed ad libitum and kept under a 12+12 h light/dark regimen, the DNA dependent RNA polymerase activity of liver cell nuclei was determined every four hours. From identical rats, nuclear non-histone protein and DNA, and cytoplasmic protein was determined by Feulgen-Naphtol Yellow S cytophotometry of isolated liver cells. The minimum: maximum ratio of the RNA polymerase activity is 0.77; the min:max ratio of nuclear non-histone protein is 0.84. These two parameters have identical time courses with a gradual decline during the light period and a sharp rise after the onset of the dark period. The variations in nuclear DNA content, estimated as the amount of Feulgen stain bound, closely parallel those of the RNA polymerase activity and nuclear non-histone protein content (min:max=0.96). The amount of cytoplasmic protein per cell also varies throughout the day, but its time curve lags behind those of nuclear nonhistone content and RNA polymerase activity. These results are consistent with the concept of nuclear non-histone proteins as de-repressors of the DNA template in differentiated, non-proliferating cells, and support the validity of using Feulgen-Naphthol Yellow S cytophotometry of nuclear non-histone proteins as an estimate of gene expression in such cells.