THE NUCLEAR SUV3-1 MUTATION AFFECTS A VARIETY OF POSTTRANSCRIPTIONAL PROCESSES IN YEAST MITOCHONDRIA

The SUV3-1 mutation was isolated earlier as a suppressor of a deletion of a conserved RNA processing site (dodecamer) near the 3′ end of the var1 gene. Previous studies Indicate that the suppressor enhances translation of mutant var1 messages; unexpectedly, It also causes over-accumulation of excised intron RNA of the large rRNA gene intron and blocks cleavage at the dodecamer site within that intron. In this study most mitochondrial genes in SUV3-1 and suv3 nuclear contexts are surveyed for changes in levels of mRNA, for Interference with dodecamer cleavage and splicing and for levels of excised intron RNAs. SUV3-1 has little or no effect on the size or abundance of unspliced RNAs tested. It results, however, In a marked Increase In the abundance of seven of eight excised group I intron RNAs tested, most of which are not detectable In wild-type (suv3) strains. The suppressor lowers levels of the cob and coxl mRNAs about 2-5 and 20-fold, respectively. The effect on coxi mRNA results from a decrease in the splicing of its intron 5β Despite the reduction in these mRNA levels, the amounts of coxi and cyt b polypeptldes were close to wild-type levels in SUV3-1 cells. These data show that the suv3 gene plays a prominent role in post-transcriptional and translation events in yeast mitochondria. © 1990 Oxford University Press.