Blogenesis of mitochondria: a mutation in the 5‘-untranslated region of yease mitochondrialolilmRNA leading to impairment in translation of subunit 9 of the mitochondrial ATPase Complex

Abstract

A temperature-conditional mit- mutant of Saccharomyces cerevisiae has been characterized; the mutant strain h45 cannot grow at 36 degrees C on nonfermentable substrates yet appears to be normal at 28 degrees C. The mutation in strain h45 maps genetically to the oli1 region of the mitochondrial DNA (mtDNA) genome, and prevents the synthesis at 36 degrees C of the oli1 gene product, subunit 9 of the mitochondrial ATPase complex. Since the level of oli1 mRNA in mutant h45 is close to normal at 36 degrees C, it is concluded that there is a specific block in translation of this mRNA at the non-permissive temperature. DNA sequence analysis of mtDNA from strain h45 reveals an additional T residue inserted 88 bp upstream of the oli1 coding region, in the A,T-rich sequence that is transcribed into the 5'-untranslated region of the oli1 mRNA. Sequence data on two revertants show that one returns to wild-type parental (J69-1B) mtDNA sequence, whilst the other contains an inserted A residue adjacent to the T inserted in the original h45 mutant. The results are discussed in terms of the stability of folds in RNA upstream of putative ribosome-binding sites in mitochondrial mRNA, and the potential action of nuclear-coded proteins that might be activators of the translation of specific mitochondrial mRNAs in yeast mitochondria.