Functions of the adenovirus E1B tumour antigens

The adenovirus E1B gene products are required for productive infection of human cells and for complete transformation of rodent cells in cooperation with the E1A gene products. Two major, unrelated polypeptides of 55,000 (55K) and 19,000 (19K) daltons are encoded by the E1B region. The 55K protein is required for efficient DNA replication, late mRNA transport to the cytoplasm and shut-off of cellular mRNA transport in productively infected cells. This protein is required for virus-mediated, but not DNA-mediated, transformation of rodent cells. It appears that the 55K protein does not directly contribute to cell transformation, but influences the oncogenicity of adenoviruses when they are inoculated into newborn hamsters. In contrast, the 19K protein is required for adenovirus induced cellular transformation and oncogenicity and localizes to membranes of the nuclear envelope, cytoplasm and the cell surface in transformed cells. This protein affects the efficiency of virus growth in some, but not all, human cells by regulating the expression of other adenovirus early genes.