Deoxyribonucleic acid-dependent ribonucleic acid polymerase activity in rat liver after protein restriction

Abstract

Rats were fed for 6 days on a diet containing either 3 or 20% high-quality protein. Nuclei were isolated from liver and DNA-dependent RNA polymerases (EC 2.7.7.6) extracted with 1 M-(NH4)2SO4. The proteins were then precipitated with 3.5 M-(NH4)2SO4 and after dialysis applied to a DEAE-Sephadex column. The column was developed with a gradient of (NH4)2SO4. Polymerase I separated well from α-amanitin-sensitive polymerase II. The enzyme activities were compared between the two dietary groups. Rats that had received 3% protein showed a lower polymerase I activity per g wet wt. of liver, per mg of DNA and per mg of protein. Polymerase II was lower in activity per g wet wt. of liver and per mg of DNA, but was higher per mg of protein. Polyacrylamide-gel electrophoretograms showed a higher proportion of contaminating proteins in polymerase II fractions isolated from 20%-protein-fed rats. The data explain the lower activity obtained per mg of protein in these rats. It is concluded that a decrease in dietary protein content from 20 to 3% induces a fall in content and specific activity of RNA polymerase I and II in liver.