Mitochondrial protein synthesis is not required for efficient excision of intron aI5 β from COX1 pre-mRNA in Saccharomyces cerevisiae

Abstract

Splicing of the group I intron aI5β from the yeast mitochondrial COX1 transcript requires at least four proteins, encoded by the nuclear genes PET54, MRS1/PET157, SUV3 and MSS18. These proteins either act directly to facilitate intron aI5β excision, or indirectly in some manner. One possible indirect mode of action of these nuclear gene products is in stimulation of expression of a mitochondrial protein, such as a maturase, that is necessary for intron aI5β excision. To test this possibility, splicing of intron aI5β was examined in a ρ⁻ strain, which is incapable of mitochondrial protein synthesis. A quantitative RT-PCR assay was set up to compare levels of spliced COX1 mRNA present in three strains: a wild–type ρ⁺ strain; the ρ⁻strain 7–49b-11, which retains the entire COX1 transcription unit; and a strain bearing a null mutation in the nuclear PET54 gene. The results showed that excision of aI5β occurs relatively efficiently in the ρ⁻ strain, and therefore does not require any mitochondrial-encoded proteins.