The data summarized in this chapter show that morphological transformation and oncogenesis by adenoviruses are brought about by the coordinated activity of regions E1A and E1B. Gene products of each of these subregions appear to fulfill distinct roles in oncogenic transformation, with the possible exception of the product(s) encoded by the O. 9-kb E1A mRNA. Also unclear is the func- tion of the 20-kd E1B protein, which has a small role, if any, in morphological transformation, but appears to be essential for the development of the oncogenic phenotype, as defined by the ability of transformed...