1 Mechanisms for Replicating DNA

Abstract

COMMON STEPS IN DNA REPLICATION In the most fundamental sense, the general mechanism of DNA replication was first suggested by Watson and Crick as an immediate and obvious consequence of the complementarity of the two strands of the DNA structure. Thus, all replication processes simply involve the melting apart of the two strands followed by the polymerization of each complementary strand on the resulting single-stranded templates. However, when one looks a bit closer at the details of the process of genome duplication, one finds that cells, plasmids, and viruses have evolved a bewildering variety of particular solutions to the problem (Kornberg and Baker 1992). In many cases, the level of complexity of the enzymatic machinery for DNA replication is considerably greater than might have been expected, given that the information required to generate two daughter genomes is encoded in the structure of the parental genome in such a simple way. Such complexity presumably evolved to increase the efficiency and fidelity of DNA replication and to ensure that the duplication of the genome is coordinated with other events in the life of a cell. Below we attempt to distill the observed complexity down to the few basic processes that are common to most DNA replication pathways. Initial Opening of the Duplex at Origins of Replication DNA replication usually begins at one or more specific sites within the genome, referred to as origins of DNA replication. The first essential event in the initiation of DNA synthesis is the local opening of the...