Mitochondrial protein-synthesizing machinery in Saccharomyces cerevisiae grown in different metabolic conditions. Variability of seryl-tRNA and alanyl-tRNA isoacceptor patterns.

1. The isoacceptor patterns of mitochondrial seryl and alanyl-tRNAs from Saccharomyces cerevisiae grown under different conditions and committed to fermentative or respiratory metabolism have been studied by reversed-phase chromatography. 2. An extensive variability of the chromatographic patterns of the four isoacceptors for serine and of the three isoacceptors for alanine has been observed as a function of carbon source and stage of growth, but the main differences were observed in the different stages of growth on glucose. 3. In order to distinguish the effects due to stage of growth from those due to relief from glucose repression, the isoacceptor patterns of mitochondrial tRNA were compared in repressed and derepressed resting cells; results show that some of the mitochondrial species are almost undetectable in resting repressed cells, but are the major ones after recovery of respiration. 4. Two of the serine isoacceptors (species 1 and 2), one of which is absent or not acylable in repressed resting cells, are different gene products.