ABSTRACT
Model systems can help considerably in furthering the understanding of complex biological processes. Viruses which have DNA as their genetic material are potentially good model systems for studying various features of cellular DNA replication. Viral genomes are relatively small, of the order of 2.5 to 100 kb, compared to the approximately 109 to 1011 bp of nuclear DNA in higher eukaryotes. Since their genomes are small, it is considered that viruses need to depend, at least to a certain extent, on host processes for their replication. The nucleotide sequences of viral DNAs can be determined relatively easily and, by studying the replication, features important at the molecular level can be understood. This philosophy has been well supported in animal systems, especially with the use of simian virus 40 (SV40) as a model system. However, as will be discussed later (Section IV), there are some reservations on the applicability of transferring information from the study of viral replication to the replication of cellular DNA.
