The long-term goal of this research project is to understand the enzymatic properties, motor properties, and cellular functions of myosin XIX (Myo19), a molecular motor protein involved in the transport and localization of mitochondria, an organelle central to multiple cellular processes. Mitochondrial dynamics have been shown to be partially actin-based, and mutations in other genes involved in mitochondrial dynamics lead to human diseases. Additionally, microarray analyses indicate that Myo19 expression is increased in certain cancers, compared to normal tissues. Previous studies show that Myo19 plays a role in mitochondrial motility in cultured cells as expression of GFP-tagged Myo19 constructs alters mitochondrial dynamics in a pulmonary cancer cell line and in a cultured neuronal cell line. Taken together, analysis of the Myo19 protein sequence and analysis of the effect of GFP-Myo19 expression in cultured cells lead to the hypothesis that Myo19 plays a role in mitochondrial dynamics, as it contains a conserved myosin motor domain and interacts with mitochondria via its tail domain. We will use both Myo19 knock-down and overexpression of functional and non-functional Myo19 constructs in cell culture models of cell division and apoptosis to determine what role Myo19 may play in each of those processes. Expression and purification of Myo19 motor domain will allow for a complete in vitro analysis of the rate and equilibrium constants associated with the motor properties of Myo19. Additionally, purified protein will be used to directly examine the motor properties of Myo19 using an in vitro actin sliding filament motility assay system. Examination of both the enzymatic and motor characteristics of Myo19 in vitro will allow the determination of the mechanism by which Myo19 motor activity generates force, and determination of factors that may regulate its function in vivo. By examining the functional roles, enzymatic properties, and motor properties, of Myo19, these proposed studies will further our understanding of mitochondrial dynamics in health and disease.