Biosynthesis of cellular and viral DNA and RNA has been a major topic in
molecular biology and biochemistry. The studies by Arthur Kornberg and
his colleagues on the in-vitro synthesis of DNA have opened new avenues
to understanding the processes controlling the duplication of the
genetic information encoded in the DNA and RNA of bacterial and
mammalian cells. Viral nucleic acids are replicated in infected cells
(bacterial, plant, and animal) by virus- coded enzymes with or without
the involvement of proteins and enzymes coded by the host cells. The
ability of the virus to replicate its genome within a relatively short
period in the infected cell makes it an excellent biological tool for
studying the molecular events in nucleic acid replication. Indeed, the
identification of a number of virus-coded proteins that participate in
the biosynthesis of X174 and SV40 DNA has led to the construction of
in-vitro systems for the study of nucleic acid biosynthesis. Similarly,
studies on the replication of other phage, animal and plant viruses have
provided an insight into the nucleic acid sequences from which DNA
synthesis is initiated, as well as the proteins and enzymes that
regulate the catalyse biosynthetic processes. Investi- gation of the
molecular processes involved in the replication of cellular and
mitochondrial genomes has gained momentum from the rapid developments in
the analyses of viral nucleic acid biosynthesis.