Relationship between the effect of O2 on energy metabolism and RNA synthesis in Rhodotorula gracilis

In the aerobic yeast Rhodotorula gracilis, a decrease in O2 availability, from saturating conditions (pO2 = 100 mm Hg) to pO2 = 1 mm Hg, causes a decrease in the growth rate accompanied by a fall in the accumulation rate of RNA and, to a lesser extent, of proteins. At pO2 = 1, no relevant changes in the levels of triphosphate nucleotides (ATP, GTP, CTP and UTP) are observed with respect to the controls, while the ADP and AMP levels markedly increase. The uptake of labelled precursors and qualitative analysis of RNA suggest that the decrease in the RNA accumulation rate at pO2 = 1 is due to a decreased RNA synthesis rate. This paper examines the mechanism by which low availability of O2 causes a decrease in the RNA synthesis rate even though total triphosphate nucleotide levels remain high.