Control of nucleolar RNA synthesis by the intracellular pool sizes of ATP and GTP.

The influence of amino acid starvation on both the pool sizes of nucleoside triphosphates and the rRNA synthetic capacity of Ehrlich ascites cells was studied. The results indicate that under shiftdown conditions, an immediate shrinkage of the cellular ATP and GTP levels occurs. Concomitant with this, protein and rRNA syntheisis are markedly inhibited. If the pool sizes of purine nucleaside triphosphates are expanded by adding adenosine or guanosine to cells cultured in histidine-free medium, the nucleolar RNA synthesis is fully restored, while protein synthesis remains inhibited. The results suggest that the rate of pre-rRNA transcription may be controlled by the actual nucleoside triphosphate levels of the cells rather than by short-lived protein(s), as has been previously postulated.