24 Adenovirus DNA Replication

Abstract

The adenovirus genome can be replicated in vitro by the combined action of three viral proteins, two cellular transcription factors, and topoisomerase I (Table 1). Early viral transcription results in expression of three viral genes, preterminal protein (pTP), DNA polymerase (Ad pol), and DNA-binding protein (DBP), that genetic evidence indicates are required for viral DNA replication. With the development of in vitro systems (Challberg and Kelly 1979), it was soon shown that cellular factors were required in addition to the three viral proteins. One of these proteins could be replaced by calf thymus topoisomerase and was required for complete elongation of the genome (Nagata et al. 1982). In contrast, the other factors were both sequence-specific DNA-binding proteins that recognized DNA within the inverted terminal repeats (ITRs) of the adenovirus genome (Nagata et al. 1983; Pruijn et al. 1986). Because all of these proteins have been cloned, overexpressed, and purified, the adenovirus genome represents one of the few eukaryotic systems in which all the components for DNA replication have been precisely defined.

Within virions, the adenovirus genome is maintained in a highly condensed form by small basic proteins, but after infection of susceptible cells, the virion is uncoated and viral DNA is released into the cell nucleus. Adenovirus genomes are linear double-stranded DNA molecules of 35–36 kb with ITRs of about 100 bp, the exact size depending on serotype. DNA replication initiates at either end of the linear 36-kbp viral genome by a protein-priming mechanism in which a covalent linkage...