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

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.