Building a career that encompasses both the worlds of basic research and patient care is of utmost importance to the applicant. He hopes to achieve this long term career goal by undertaking intensive research training, following completion of his clinical fellowship training in hematology/oncology. However, substantive contributions from the bench will require limited clinical exposure from hereon. Thus, the applicant's immediate career goal is to continue his basic research training, in the process addressing the questions outlined in this proposal. The training environment and the project undertaken are ideally suited to provide the technical training and develop the critical thinking skills necessary to reach this coal. Regarding the former, Dr. Goldberg is one of three senior investigators whose labs meet on a weekly basis for journal club and to present data. These groups have broad common interests but varied areas of expertise, thus providing vital exposure to various perspectives and new techniques, and feedback on the applicant's work. Regarding the latter, this proposal uses Saccharomyces cerevisiae as a model eukaryotic system to address the fundamental biologic question of how cells sense hypoxia. This ability is crucial to a cell's survival, and at the molecular level is mediated in large part by alterations in gene expression. Although several mammalian genes are upregulated by hypoxia, the mechanism of oxygen (02) sensing is poorly understood. Identifying the genes that comprise the 02 sensing pathway(s) in eukaryotes is a difficult problem to approach in diploid cells. Therefore, this proposal uses the haploid yeast, S. cerevisiae, to address this question. Evidence exists that the mechanism of hypoxic adaptation is highly conserved. Thus, regulatory elements of previously identified hypoxia-regulated yeast genes fused to a reporter gene will be used as an assay system: i) to identify yeast genes involved in the O2 sensing pathway using standard yeast genetic techniques, and ii) to test the hypothesis that the recently cloned yeast flavohemoglobin functions as an O2 sensor by performing gene disruption studies and examining the subsequent phenotype. Understanding the molecular mechanisms needed to respond to hypoxic stress is crucial in designing rational strategies to treat a host of human diseases, such as cancer and ischemic cardiac and neurologic disease, where relative cellular hypoxia is a vital component of disease pathogenesis.