Initiation of Viral DNA Replication

This chapter focuses on the mechanisms involved in initiation of animal virus DNA replication. This step is of fundamental importance because it represents the central point of control of the replication process. Two of the best-characterized viruses, adenovirus and SV40, are discussed as examples of viruses that normally multiply by productive cytocidal infection. In these two cases viral DNA replication begins soon after infection and continues at a high rate until the death of the host cell. Two other viruses—bovine papilloma virus and Epstein-Barr virus—are presented in the chapter as examples of viruses that are capable of multiplying as stable extrachromosomal plasmids. In these two cases viral DNA replication is precisely controlled so that the number of viral genomes doubles only once per cell cycle and under normal circumstances the host is not killed. All virus groups described in this chapter—as well as most of the remaining virus groups (the poxviruses may constitute an exception)—initiate DNA replication in specific regions of the viral chromosome referred to as origins of replication. There appears to be little nucleotide sequence homology among the origins of the various virus groups, although there are some general structural features common to many animal virus origins and to a number of prokaryotic origins as well. These include the presence of large palindromic sequences and extensive A/T-rich blocks.