Abstract

A new gene essential for cell viability and indispensable for the biogenesis of a functional respiratory chain in Saccharomyces cerevisiae was isolated by complementing a temperature-sensitive mutant. This conditional nuclear mutation selectively affects oxidative phosphorylation at restrictive temperatures. At the molecular level a severe and complex defect inside mitochondria is observed, with drastically reduced levels of mitochondrial transcripts. Surprisingly a null mutation in this nuclear gene in a haploid yeast strain leads to cell death. Spores containing a disrupted copy of the gene exhibit a severe growth defect and cell division stops irreversibly after 3 to 4 days. It is shown that the null and conditional mutants are indeed allelic. This finding demonstrates a dual function of the gene product in oxidative phosphorylation and vegetative growth. The putative protein product, as deduced from the sequence of the relevant reading frame is characterized by a low molecular weight of approximately 14 kDa, a high content of charged amino acids and a very low codon bias index. A transcript of low abundance and with a length of about 600 nucleotides can be assigned to this gene.