Nuclear migration through the cytoplasm occurs in organisms from fungi to man and is required for the growth and proper development of most eukaryotes. Our laboratory has been studying the molecular genetics of nuclear migration in a simple eukaryote, the filamentous fungus Aspergillus nidulans. To date we have identified fourteen "nud" (nuclear distribution) genes whose products are involved in nuclear migration and have cloned and characterized seven of them. All are evolutionarily conserved. Some are components of the molecular motor cytoplasmic dynein. Others are components of dynactin, a protein complex thought to couple the dynein motor to membrane-bounded cargo. Still other nud gene products are components of neither dynein or dynactin, but presumably are proteins that play a regulatory or as yet unknown structural role in nuclear migration. One of these nud gene products, NUDF, is particularly fascinating because a deficiency of its human homolog, LIS 1, causes lissencephaly, a genetic disease in which neurons fail to migrate properly from the paraventricular proliferative zone of the brain to the cerebral cortex. Because nuclear migration occurs in neurons and has been described to be an important component of cell migration in certain cancer cells that undergo nucleokinesis, we have proposed that the failure of neuronal migration in lissencephaly is really a failure of nuclear migration. Evidence from a LIS 1 knockout mouse supports this conclusion. The main thrust of this application is to determine how the NUDF protein affects nuclear migration by analyzing its effects on the function of the cytoplasmic dynein motor, the dynactin coupling machinery, and on the microtubule track with which the motor interacts in vivo and in vitro, using wild-type and nud mutant strains of Aspergillus.