A nuclear mutation affecting mitochondrial transcription in Saccharomyces cerevisiae

Mitochondrial transcription was studied in a nuclear temperature-sensitive pet mutant of Saccharomyces cerevisiae. The mitochondrial RNA levels in vivo and the in vitro transcriptional activities of isolated mitochondria were analysed. In comparison to the wild-type an overall reduction of mitochondrial gene expression together with a changed expression pattern was observed for the mutant, indicating a defect in mitochondrial RNA synthesis. These findings were supported by studies with a purified DNA-protein complex from yeast mitochondria. This complex was able to synthesize ribosomal and messenger RNAs in an in vitro system. Proteins from wild-type and mutant transcription complexes were tested for their DNA-binding abilities; one of the proteins identified in the wild type had either lost this ability or was absent in the mutant.