The Role of the E1b Gene Products of Adenovirus Serotype 12 in Lytic Infection and Transformation

Abstract

<p>It is well documented that two regions of the human adenoviruses, each encoding multiple polypeptides, are responsible for the transforming activity of these viruses and that these genes are essential for the efficient production of virus in permissively infected cells. This study was undertaken to examine the importance of the individual proteins of one of these regions from adenovirus serotype 12 (Ad12), the E1b region, in lytic infection and transformation. Molecular defects have been identified in the smaller protein, the 19K, in two of the cytocidal (cyt) mutants of Ad12. Direct evidence has been obtained demonstrating that the point mutation in the 19K of one of the mutants is sufficient to cause the degradation of DNA in infected KB cells and reduce the transforming activity of the mutant virus and perhaps its tumourigenic potential, which are characteristic phenotypes of the cyt mutants. A mutation was also engineered in the larger, 55K E1b protein and was found to impair viral DNA replication, reduce the expression of the late, structural proteins of the virus and block the inhibition of cellular protein synthesis which is normally observed upon infection of KB cells with the wild type virus. The 55K was also found to be necessary for the efficient expression of the early genes of the virus, particularly the E2b gene, which encodes essential proteins for viral DNA replication. The multiplicity dependent leakiness of the DNA replication defect of this mutant was exploited to separate the DNA replication defect from the defects in late protein expression and shut off of host protein synthesis. The observation that this mutant exhibited 1% of the transforming activity of the wild type virus but that transformants were fully tumourigenic also separated a transformation function from a tumourigenic function of this protein.</p>