Altered mitochondrial ribosomes in a cold-sensitive mutant of Saccharomyces cerevisiae.

A mutation at a new locus denoted tsr1 which lies very close to the ery1 locus and 21S rRNA gene in mitochondrial DNA of Saccharomyces cerevisiae, confers conditional respiratory deficiency on cells grown at low temperature, namely 18 degrees. Studies on mitochondria isolated from a strain carrying the mutatated tsr1 locus demonstrate that the rate of mitochondrial protein synthesis is cold-senitive at 18 degrees. The large subunit of the mitochondrial ribosomes isolated from the mutant strain is unstable during extraction and the isolated ribosomes are shown to be defective in catalyzing the poly U-directed synthesis of polyphenylalanine. It is concluded that the tsr1 locus is involved in the determination of the properties of the large subunit of the mitochondrial ribosome.