Two Distinct Triggers for Cycling of the Lagging Strand Polymerase at the Replication Fork

• Published in: The Journal of biological chemistry Vol. 275; no. 44; pp. 34757 - 34765
• Main Authors: Li, Xiaojun, Marians, Kenneth J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03-11-2000; American Society for Biochemistry and Molecular Biology
• Subjects: Base Sequence; DNA Polymerase III - metabolism; DNA Primers; DNA Replication; Escherichia coli; replication forks; repliction forks
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M006556200

There are two modes of DNA synthesis at a replication fork. The leading strand is synthesized in a continuous fashion in lengths that in Escherichia coli can be in excess of 2 megabases. On the other hand, the lagging strand is synthesized in relatively short stretches of 2 kilobases. Nevertheless, identical assemblies of the DNA polymerase III core tethered to the β sliding clamp account for both modes of DNA synthesis. Yet the same lagging strand polymerase accounts for the synthesis of all Okazaki fragments at a replication fork, cycling repeatedly every 1 or 2 s from the 3′-end of the just-completed fragment to the 3′-end of the new primer. Several models have been invoked to account for the rapid cycling of a polymerase complex that can remain bound to the template for upward of 40 min. By using isolated replication protein-DNA template complexes, we have tested these models and show here that cycling of the lagging strand polymerase can be triggered by either the action of primase binding to the replisome and synthesizing a primer or by collision of the lagging strand polymerase with the 5′-end of the previous Okazaki fragment.