AbstractA eukaryotic cell is compartmenatized into cellular organelles that perform specific roles in the cell. Individual cellular organelles are usually enclosed by biological membranes. One of the key organelles is mitochondrion that acts as a cellular respiratory and energy powerhouse. All cell membranes are formed by lipid bilayers containing proteins with different functions and structures. Membrane lipids are not only passive structural compoments of the membrane. They have great influence on membrane phospholipids thus regulating many cellular processes. Cardiolipin (CL) is a unique anionic phospholipid, typical for the inner mitochondrial membrane. In the first part of this PhD. project we studied regulatory mechanisms involved in the control of phosphatidylglycerol (PG), a direct precursor to CL. We found that elevated acitivity of phosphatidylglycerol phosphate synthase (Pgs1p) in the absence of inositol is responsible for observed increase of PG when Pgc1 degradation pathway is inactivated. Pgc1 protein itself is not regulated by inositol. Pgc1p activity was only slightly increased under conditions that favour mitochondrial biogenesis, e.g. when cells where grown on non-fermentable source of carbon. In the second part of the project we studied biosynthesis of CL and its regulation in Schizosaccharomyces pombe. We identified and characterised the gene encoding CL synthase, an enzyme catalyzing conversion of PG to CL. S. pombe CL synthase is a part of a mitochondrial tandem protein with a unique regulation. Tandem mitochondrial proteins are usually composed of two proteins encoded by a single gene. This gene is transcribed into one mRNA and translated into one polypeptide on cytosolic ribosomes. Fusion protein is then imported into mitochondria where it is cleaved into ist constituents. We showed that relative expression of partners of mitochondrial tandem protein consisting of CL synthase and mitochondrial hydrolase with yet unknown function is ensured by specific intron retention. Presence of this intron in mRNA is required for translation of CL synthase. This mechanism of diferential expression of partners of a mitochondrial tandem protein is novel and was not described so far.