THE SACCHAROMYCES-CEREVISIAE NUCLEAR GENE SUV3 ENCODING A PUTATIVE RNA HELICASE IS NECESSARY FOR THE STABILITY OF MITOCHONDRIAL TRANSCRIPTSCONTAINING MULTIPLE INTRONS

The product of the nuclear gene SUV3 is implicated in a variety of pos t-transcriptional processes in yeast mitochondria. We have analysed th e effect of SUV3 gene-disruption on the expression of intron-containin g alleles of the mitochondrial cytb and cox1 genes. We have constructe d several strains with mitochondrial genomes containing different comb inations of cytb and cox1 introns, and associated these genomes with t he disruption of SUV3. The resulting strains were tested for their res piratory competence and spectral cytochrome content. All the strains c ontaining only two or three introns showed normal expression of cytb a nd cox1, whereas the strains containing more introns were unable to ex press the appropriate gene. The analysis of mitochondrial RNAs by Nort hern hybridisation showed that the loss of respiratory competence in t he strains containing more introns is due to the decrease of mRNA leve l with no over-accumulation of high-molecular-weight precursors. Howev er, the transcription of the genes was not affected. These results led us to the notion that SUV3 is required for the stability of intron-co ntaining cytb and cox1 transcripts in a cumulative way, not dependent on any particular intron.