8 Structure and Genomic Organization of Adenoviruses

Abstract

Adenoviruses and papovaviruses are similar in many ways:They are nonenveloped particles with icosahedral symmetry that contain genomes of double-stranded (DS) DNA. Both replicate efficiently in vitro only in cells derived from that species of animal to which they are endemic. During lytic infection, there is an ordered expression of viral genes, with some virus-coded products synthesized at all times and others only during the late stages. Progeny virions are assembled in the nuclei of permissive cells. Nonpermissive cells become transformed following infection with papovaviruses or adenoviruses—a process which, in both cases, involves only a subset of viral genes. Transformed cells contain virus-specific antigens, viral RNA, and sequences of viral DNA covalently attached to those of the cell. At least some strains of papovaviruses and adenoviruses induce tumors in newborn rodents. If we look deeper, differences between the two groups of viruses begin to emerge. First, in contrast to the papovaviruses with their small circular DNAs, the genome of adenoviruses is a linear duplex DNA molecule (m.w. 20 × 10 6 –25 × 10 6 ) that codes for 20–30 polypeptides; at least 15 of these are incorporated into viral particles, which are morphologically complex and the products of a sophisticated assembly process. Second, whereas infectious virus can be rescued from many lines of cells transformed by papovaviruses, all attempts to rescue adenovirus from transformed cells have failed. Finally, adenoviruses and papovaviruses have very different natural histories. SV40 and polyoma virus seem not to...