RESPONSE OF POLY(ADENYLIC ACID) POLYMERASE IN RAT-LIVER NUCLEI AND MITOCHONDRIA TO STARVATION AND RE-FEEDING WITH AMINO-ACIDS

Poly(adenylic acid) polymerase was extracted from liver nuclei and mitochondria of rats either fed ad lib, starved overnight or starved and then re-fed with a complete amino acid mixture for 1-3 h. The enzymes were partially purified and assayed by using exogenous primers. Starvation resulted in an 80% decrease in the total activity of the purified nuclear enzyme, and the mitochondrial enzyme activity diminished to almost 0 after overnight starvation. Measurements of the protein content of whole nuclei or mitochondria and of the enzyme extracts from these organelles indicates that the decrease in enzyme activity on starvation was not caused by incomplete extraction of the enzyme from the starved animals. Re-feeding the animals with the complete amino acid mixture increased the total activity of poly(A) polymerase from the nuclei and mitochondria by 1.9-fold and 63-fold respectively. Under these conditions, the total protein content of the nuclei and mitochondria increased by only 13 and 32% respectively. These data indicate that poly(A) polymerase is one of the cellular proteins specifically regulated by amino acid supply.