Transcriptional regulation of the mitochondrial genome of yeast Saccharomyces cerevisiae.

The relative rates of transcription of several classes of the mitochondrial genes of the yeast Saccharomyces cerevisiae have been determined. The rates were measured by pulse labeling whole yeast with [32P]O4, isolating the total RNA, hybridization to single-stranded M13 DNA probes containing segments of the gene of interest, digestion with RNase A or T1, and separation of the protected fragment by gel electrophoresis. This analysis indicated that, among the genes analyzed, transcriptional promoters varied in strength by 20-fold while the rates of transcription varied by more than 50-fold. The strengths of the promoters of the genes were ordered: tRNAMetf greater than tRNAPhe greater than 14 S rRNA greater than 21 S rRNA greater than tRNAGlu greater than Oli-1 much greater than tRNACys. In addition, transcription rates were measured within polygenic transcription units. This analysis indicated that there was transcriptional attenuation within all the polygenic transcription units with the greatest attenuation factor being as much as 17-fold, occurring after the tRNAGlu and tRNAMetf genes. This analysis indicated that regulation of the rates of transcription in the yeast mitochondrial genome occurs by two distinct mechanisms, modulation of the rate of transcriptional initiation and attenuation of transcriptional elongation.