The overall aim of this project is to use genetic and molecular approaches to define the functions that the various type 12 E1 proteins play in transforming mouse and rat cells in vitro, and to understand the basis for the striking differences in viral oncogenicity between this serotype and non-oncogenic type 5. Our specific aims over the next three years are: 1) To extend genetic and biochemical characterization of the host-range (hr) mutants of type 12 which we have recently isolated. 2) To isolate and characterize conditional transformation-defective mutants of this serotype. 3) To isolate and characterize site-specific mutants of type 12, particularly those which alter E1A mRNA splice junctions. 4) To isolate type 12 transformants of A549 cells. 5) To analyze the transformation process in mouse kidney cells, and determine if epithelial and fibroblastic subpopulations are transformed at different frequencies. 6) Extend our study of viral oncogenicity and cellular malignancy by testing the ability of hr mutants to induce tumors and tumor specific transplantation immunity. 7) Using type 12 hr mutants, develop a complementing system for isolation and growth of non-conditionally defective mutants.