The objective of this proposal is to examine the nature of host intracellular control of viral replication which determines whether infection by a papovavirus will lead to cell death or transformation. This objective is based on the observation frequently cited in the literature that whether a cell is killed or transformed by these viruses is determined by the cell infected rather than by the virus. The general methodology will be to isolate homogeneous populations of non-permissive and permissive cells and then to determine the fate of viral DNA synthesis in each type of cell. The cellular effect on viral replication will be monitored biochemically, and the molecular basis of the difference between the cell types will be defined.