| The mitochondrial compartment is the site of oxidative phosphorylation and numerous other metabolic processes and is required for cell viability, even when the compartment is compromised by the loss of the mitochondrial genome (mtDNA). An essential feature of mitochondria is an energized inner mitochondrial membrane, which allows for insertion of key proteins and, depending on environmental and genetic conditions, the synthesis of ATP4- from ADP3- and Pi. Cells that contain an intact mitochondrial genome, referred to as rho+, can generate an energized inner membrane by creating a membrane potential (DeltaPsi M) in three ways: (1) pumping protons into the intermembrane space (IMS) as electrons are passed to O2 via the electron transport chain, (2) coupling the pumping of protons into the IMS to ATP hydrolysis by the F1FO-ATPase, and (3) exchanging ATP 4- for ADP3- through the ADP/ATP carrier (Aac). Because four subunits of the electron transport chain and three subunits of the F O portion of the F1FO-ATPase are encoded by mtDNA, viable cells lacking a mitochondrial genome (rho- cells) must maintain DeltaPsiM by exchange of ATP4- for ADP3- through Aac. ADP3- is provided by the hydrolysis of ATP4-, catalyzed by the remaining F 1 portion of the ATPase (F1-ATPase). Utilizing the growth of yeast lacking mtDNA as a phenotype for genetic approaches led to the isolation of a novel spontaneous suppressing mutation that changed a conserved residue near the active site of F1-ATPase, leading to a more active, Atp3-deficient yeast F1-ATPase (Chapter 2) and allowed for the determination of the important differences between the yeast ADP/ATP carriers encoded by two paralogs, AAC1 and AAC2 (Chapters 3 and 4). |
