Htd2p/Yhr067p is a yeast 3‐hydroxyacyl‐ACP dehydratase essential for mitochondrial function and morphology

Summary Among the recently recognized aspects of mitochondrial functions, in yeast as well as humans, is their ability to synthesize fatty acids in a malonyl‐CoA dependent manner. We describe here the identification of the 3‐hydroxyacyl‐ACP dehydratase involved in mitochondrial fatty acid synthesis. A colony‐colour‐sectoring screen was applied in Saccharomyces cerevisiae in a search for mutants that, when grown on a non‐fermentable carbon source, were unable to lose a plasmid that carried a chimeric construct coding for mitochondrially localized bacterial analogue. Our mutants, which are respiratory deficient, lack cytochromes and display abnormal mitochondrial morphology, were found to have a lesion in the yeast YHR067w/RMD12 gene. The Yhr067p is predicted to be a member of the thioesterase/thioester dehydratase‐isomerase superfamily enzymes. Hydratase 2 activity in mitochondrial extracts from cells overexpressing YHR067w was increased. These overexpressing cells also display a striking mitochondrial enlargement phenotype. We conclude that YHR067w encodes a novel mitochondrial 3‐hydroxyacyl‐thioester dehydratase 2 and suggest renaming it HTD2. The mitochondrial phenotypes of the null and overexpression mutants suggest a crucial role of YHR067w in maintenance of mitochondrial respiratory competence and morphology in yeast.