Several crucial oncoprotein interactions occur largely in tumour cells and thus provide ideal targets for intervention. The proposed project is to develop a model system for a target-specific therapy of leukaemia. The ability to isolate specific blockers of particular protein/protein interactions also provides an opportunity to uncouple complex genetic pathways in mammalian systems, which are relatively intractable to genetic analysis. The dissection of pathways using specific blockers may ultimately provide a useful avenue for identifying and characterizing new drug targets. We have chosen to target one of the known interactions of the oncoprotein, PLZF in the search for specific inhibitors. Complexes containing PLZF are involved in the development of Acute Promyelocytic Leukemia (APL) and Acute Myeloid Leukemia (AML). A genetic selection will be used to identify naturally derived peptide sequences which are capable of blocking PLZF/ETO interactions and which do not interfere with other interactions involving the PLZF protein. This technique termed 'dual-bait/reporter reverse two hybrid screening' allows one to select for or against specific blockers of known interactions in yeast cells. The affinity and specificity of the interaction blockers derived from the screen will be determined using the novel yeast genetic system and by ex vivo assays of functional effects of candidate peptides on repression and growth inhibitory activity of PLZF. Finally, isolation of specific blockers of PLZF interactions may provide leads or the development of new therapeutic agents for the treatment of APL and AML.