Schizosaccharomyces pombe Sls1 is primarily required for cox1 mRNA translation

Mitochondrial DNA (mtDNA) encodes essential subunits of the oxidative phosphorylation (OXPHOS) complexes; thus, the expression of mtDNA-encoded genes is essential for the synthesis of adenosine triphosphate. However, factors involved in mitochondrial translation have not been fully characterized. In this study, we characterized Schizosaccharomyces pombe Sls1, which has sequence similarity to Saccharomyces cerevisiae Sls1 that is required for the translation of all mtDNA-encoded messenger RNAs (mRNAs). Deletion of S. pombe sls1 severely impaired the growth of the cells on a rich medium containing the nonfermentable carbon source glycerol, which requires mitochondrial respiration. We found that the translation of mtDNA-encoded Cox1, the largest subunit of the cytochrome c oxidase complex, was severely impaired in Delta sls1 cells. Deletion of S. pombe sls1 also resulted in a barely detectable steady-state level of mature cox1 mRNA. RNA immunoprecipitation showed that S. pombe Sls1 interacts with cox1 mRNA. Sucrose gradient sedimentation analysis revealed that S. pombe Sls1 is associated with the small subunit of mitochondrial ribosomes. Our results suggest that unlike S. cerevisiae Sls1, S. pombe Sls1 is primarily required for the accumulation and translation of cox1 mRNA.