Genome-wide deletion mutant analysis reveals genes required for respiratory growth, mitochondrial genome maintenance and mitochondrial protein synthesis in Saccharomyces cerevisiae.

BACKGROUND: The mitochondrial respiratory chain produces metabolic energy by oxidative phosphorylation. Biogenesis of the respiratory chain requires the coordinated expression of two genomes: the nuclear genome encoding the vast majority of mitochondrial proteins, and the mitochondrial genome encoding a handful of mitochondrial proteins. The understanding of the molecular processes contributing to respiratory chain assembly and maintenance requires the systematic identification and functional analysis of the genes involved. RESULTS: We pursued a systematic, genome-wide approach to define the sets of genes required for respiratory activity and maintenance and expression of the mitochondrial genome in yeast. By comparative gene deletion analysis we found an unexpected phenotypic plasticity among respiratory-deficient mutants, and we identified ten previously uncharacterized genes essential for respiratory growth (RRG1 through RRG10). Systematic functional analysis of 319 respiratory-deficient mutants revealed 16 genes essential for maintenance of the mitochondrial genome, 88 genes required for mitochondrial protein translation, and 10 genes required for expression of specific mitochondrial gene products. A group of mutants acquiring irreversible damage compromising respiratory capacity includes strains defective in assembly of the cytochrome c oxidase that were found to be particularly sensitive to aging. CONCLUSIONS: These data advance the understanding of the molecular processes contributing to maintenance of the mitochondrial genome, mitochondrial protein translation, and assembly of the respiratory chain. They revealed a number of previously uncharacterized components, and provide a comprehensive picture of the molecular processes required for respiratory activity in a simple eukaryotic cell.

Molecular machinery of mitochondrial dynamics in yeast.

Mitochondria are amazingly dynamic organelles. They continuously move along cytoskeletal tracks and frequently fuse and divide. These processes are important for maintenance of mitochondrial functions, for inheritance of the organelles upon cell division, for cellular differentiation and for apoptosis. As the machinery of mitochondrial behavior has been highly conserved during evolution, it can be studied in simple model organisms, such as yeast. During the past decade, several key components of mitochondrial dynamics have been identified and functionally characterized in Saccharomyces cerevisiae. These include the mitochondrial fusion and fission machineries and proteins required for maintenance of tubular shape and mitochondrial motility. Taken together, these findings reveal a comprehensive picture that shows the cellular processes and molecular components required for mitochondrial inheritance and morphogenesis in a simple eukaryotic cell.

Nonredundant roles of mitochondria-associated F-box proteins Mfb1 and Mdm30 in maintenance of mitochondrial morphology in yeast.

Mitochondria constantly fuse and divide to adapt organellar morphology to the cell's ever-changing physiological conditions. Little is known about the molecular mechanisms regulating mitochondrial dynamics. F-box proteins are subunits of both Skp1-Cullin-F-box (SCF) ubiquitin ligases and non-SCF complexes that regulate a large number of cellular processes. Here, we analyzed the roles of two yeast F-box proteins, Mfb1 and Mdm30, in mitochondrial dynamics. Mfb1 is a novel mitochondria-associated F-box protein. Mitochondria in mutants lacking Mfb1 are fusion competent, but they form aberrant aggregates of interconnected tubules. In contrast, mitochondria in mutants lacking Mdm30 are highly fragmented due to a defect in mitochondrial fusion. Fragmented mitochondria are docked but nonfused in Deltamdm30 cells. Mitochondrial fusion is also blocked during sporulation of homozygous diploid mutants lacking Mdm30, leading to a mitochondrial inheritance defect in ascospores. Mfb1 and Mdm30 exert nonredundant functions and likely have different target proteins. Because defects in F-box protein mutants could not be mimicked by depletion of SCF complex and proteasome core subunits, additional yet unknown factors are likely involved in regulating mitochondrial dynamics. We propose that mitochondria-associated F-box proteins Mfb1 and Mdm30 are key components of a complex machinery that regulates mitochondrial dynamics throughout yeast's entire life cycle.

Functional analysis of the allatostatin-A type gene in the cricket Gryllus bimaculatus and the armyworm Spodoptera frugiperda.

Double-stranded RNA (dsRNA) gene interference is an efficient method to silence gene expression in a sequence specific manner. Here we show, that dsRNA targeting the allatostatin (AS)-A type (FGL/I/V-amide) gene of Gryllus bimaculatus (Ensifera, Gryllidae) and Spodoptera frugiperda (Lepidoptera, Noctuidae) injected into freshly moulted larvae or adult crickets and moths produced a rapid and long-lasting reduction in the mRNA levels in various tissues. The effect lasted up to 7 days. Following dsRNA injection, the juvenile hormone (JH) titers in the hemolymph were clearly raised in both species. AS-dsRNA injection induced a reduced body weight in larval and adult crickets and the imaginal moult was incomplete. Silencing allatostatin type-A expression also reduced the egg and testes development in crickets, and the oviposition rate was drastically diminished in both species.