Suppression of a yeast mitochondrial RNA processing defect by nuclear mutations

Abstract

The S. cerevisiae strain h56 is a temperature-sensitive mit ^- mutant containing a single nucleotide substitution in the region 5′ to the reading frame of the mitochondrial var1 gene. The mutation decreases the efficiency of processing of a precursor RNA such that little var1 mRNA is produced at the restrictive temperature, 36°C. This communication reports the isolation and characterization of several strains carrying nuclear mutations which suppress the temperature-sensitivity of h56. Both dominant and recessive suppressor mutations were isolated. One dominant suppressor strain (h56-S4) was characterized biochemically, and the mechanism of suppression shown to involve a restoration of precursor RNA processing at the restrictive temperature, with a concomitant increase in the synthesis of the var1 protein. It appears likely that the suppressing allele encodes a component of an RNA processing endoribonuclease active on var1 transcripts. A genomic library was constructed from the h56-S4 strain, and several plasmids showing suppressed activity were isolated. A preliminary analysis of these plasmids is presented.