Ccm1p/Ygr150cp, a pentatricopeptide repeat protein, is essential to remove the fourth intron of both COB and COX1 pre-mRNAs in Saccharomyces cerevisiae

YGR150C gene product (Ygr150cp) is one of the three mitochondrially located Saccharomyces cerevisiae proteins with pentatricopeptide repeat (PPR) motifs. Ygr150cp is essential for mitochondrial functionality but its molecular targets are still unknown. This study was undertaken to define the role of Ygr150cp in mitochondria biogenesis. Repression of Ygr150cp expression in complemented mutants prevented their use of glycerol or lactate, but allowed limited growth on ethanol-containing medium. RNA hybridization studies showed that Delta ygr150c meiotic segregants produced COB and COX1 transcripts but failed to process them into the mature forms. Detailed RT-PCR assays revealed that Delta ygr150c specifically failed to remove the fourth intron of both COB and COX1 pre-mRNAs while all other group I introns were excised. Expression of Ygr150cp mutants without any of the PPR motifs did not complement the growth phenotype. Accordingly, we designate YGR150C as CCM1 (COB and COX1 mRNA maturation). This report provides the first evidence of PPR protein involvement in the specific removal of group I introns in mitochondria of S. cerevisiae.