The long-term objectives of this project are to investigate the pathogenesis of human leukemias through studies of the HRX gene which is structurally altered in a diverse subset with karyotypic abnormalities of chromosome band 11q23. Translocations of HRX cause its fusion with a wide variety of heterologous genes resulting in the synthesis of chimeric proteins. These studies will characterize the potential transcriptional and transforming properties of HRX fusion proteins induced by chromosomal translocations in acute leukemias. The studies proposed in Aim#1 will establish experimental models for investigation of leukemias with 11q23 translocations. Transforming properties of HRX chimeric proteins will be demonstrated and characterized in cultured cell lines stably transfected with various constructs expressing HRX fusion cDNAs. Structure/function experiments employing mutant HRX fusion genes in the lymphoid or myeloid lineages will be constructed and characterized for in vivo pathologic states associated with expression of HRX candidate oncogenes and to obtain animal models for HRX- induced leukemias. Aims #2 and #3 address the hypothesis that leukemogenesis induced by HRX chimeric proteins results from alterations of transcriptional processes in cells with translocations of band 11q23. Functional domains of HRX and its fusion partners ENL and FEL will be characterized using transactivation assays in transiently transfected cell liens. Binding site selection assays will establish DNA sequences bound by the portion of HRX retained in 11q23-induced chimeras. Structure/function assays will correlate the transcriptional and transforming properties of HRX chimeric proteins. A yeast interactional cloning system will be employed to identify proteins that interact with HRX or its fusion partners. These studies should have important implications for our understanding of leukemogenesis in general. They should provide insights into the early cellular changes that underlie a major form of human cancer. They will provide reagents for improved diagnosis and longitudinal assessment of patients with leukemia. It is likely that these studies will also yield an increased fund of knowledge concerning the biological features of leukemic cell growth and result in animal models for testing newer generations of anti-leukemic drugs.