Metabolism of ribonucleic acid during respiratory adaptation of yeast

Abstract

1. (1) The RNA metabolism of non-growing yeast undergoing oxygen-induced respiratory adaptation was compared to that of non-adapting cells. 2. (2) No difference in the rate of RNA synthesis was observed. A marked stimulation in the rate of [ 14C]uracil incorporation into RNA during adaptation was attributed to increased rate of entry of the precursor into the nucleotide pool. 3. (3) No qualitative differences in the most rapidly labelled RNA fraction were found. In both cases the RNA was extremely heterogeneous in molecular size (mean value 10–22 S) and distinct from ribosomal and soluble RNA. The technique for isolation of non-degraded yeast RNA was given. The base composition resembled neither the bulk RNA nor the DNA, nor was it an intermediate type; it was characterized by low G/A and U/A ratios. 4. (4) Differences were detected in the fate of the RNA when exposure to precursors was prolonged. (a) In both cases the RNA underwent rapid changes in molecular size distribution towards that of the ribosomal and soluble RNA. (b) In adapting cells a rapid change in base composition towards that of the bulk RNA was observed; there was evidence for marked heterogeneity within the accumulating fraction. In non-adapting cells the base-composition change was more restricted; intermediate RNA forms were detected, resembling ribosomal RNA in molecular size but with quite different base composition. (c) There was an increased transfer of RNA to the ribosomal fraction in adapting cells. (d) In non-adapting cells much of the RNA found was unstable. No instability was detected in adapting cells, the first formed RNA acting as a precursor of the more stable forms.