The use of animal viruses as model systems for probing the complexities of molecular control mechanisms has been particularly fruitful. It is generally thought that understanding of genetic regulation in viruses will provide an insight into similar processes in eukaryotic cells. The overall objective of our research is to systematically develop our understanding of gene regulation in virus infected cells and to use this knowledge for developing in vitro systems from which activities can be purified and characterized. In the present renewed application we specifically intend to accomplish the following: 1) To characterize the structure of the actively transcribed viral minichromosomes and the role of minichromosome associated proteins in the regulation of transcription. 2) To test and substantiate our recently published model (Hay, N., Skolnik-David, H. and Aloni, Y. Cell 29, 183-193, 1982) for quantitative regulation of the synthesis of SV40 capsid proteins by attenuation and mRNA modulation in a feedback control mechanism. 3) To determine the role of the nuclear matrix and cytoskeleton in virus assembly and in the biogenesis of viral RNA. 4) To study the mechanism of transcription-termination, RNA processing, polyadenylation and splicing. The acquisition of knowledge by the present research will ultimately contribute to a better understanding of the more complex phenomena in mammalian cells, such as molecular process of differentiation, development and malignant transformation.