Adenovirus DNA Replication
Muralidhara Ramachandra and R. Padmanabhan
After adenovirus (Ad) enters the cell by receptor-mediated endocytosis, the viral DNA is uncoated and transported to the nucleus. Beginning at 6-8 hours post-infection, DNA is efficiently replicated, generating high amounts of progeny molecules (105-106/cell). Development of a cell-free system has contributed greatly to our understanding of viral DNA replication (for reviews see refs. 2,3). DNA replication results from an orderly interaction between viral proteins, cellular factors and template DNA at discrete sites within the nucleus that appear to be distinct from the transcription sites. DNA synthesis begins by a novel protein priming mechanism in which viral polymerase (AdPol) catalyzes the covalent linkage of the 5´-terminal nucleotide dCMP to the β-OH of a serine residue of the viral preterminal protein (pTP), which is the precursor of the terminal protein (TP). This initiation of DNA replication occurs at specific DNA sequences at the origin of replication in the presence of cellular transcription factors, nuclear factor I (NF-I) or CAAT transcription factor (CTF-1) and nuclear factor III (NF-III) or octomer-binding transcription factor (Oct-1). The pTP-dCMP complex formed in the initiation reaction serves as the primer for subsequent elongation catalyzed by AdPol via a strand displacement mechanism in the presence of the virus-encoded DNA-binding protein (DBP) and the host factor, nuclear factor II (NF-II), which is a type I DNA topoisomerase.