Pif1-Family Helicases Support Fork Convergence during DNA Replication Termination in Eukaryotes

• Published in: Molecular cell 2019-04, Vol.74 (2), p.231-244.e9
• Main Authors: Deegan, Tom D., Baxter, Jonathan, Ortiz Bazán, María Ángeles, Yeeles, Joseph T.P., Labib, Karim P.M.
• Format: Article
• Language: English
• Subjects: chromosome replication; CMG helicase; DNA helicases; DNA Helicases - genetics; DNA replication; DNA Replication - genetics; DNA replication termination; DNA Topoisomerases - genetics; Escherichia coli; Escherichia coli - genetics; Eukaryota - genetics; eukaryotic cells; fork convergence; Genomic Instability; Pif1; plasmids; Plasmids - genetics; replisome; Rrm3; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae Proteins - genetics; Top2; topoisomerase; yeasts
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2019.01.040

The convergence of two DNA replication forks creates unique problems during DNA replication termination. In E. coli and SV40, the release of torsional strain by type II topoisomerases is critical for converging replisomes to complete DNA synthesis, but the pathways that mediate fork convergence in eukaryotes are unknown. We studied the convergence of reconstituted yeast replication forks that include all core replisome components and both type I and type II topoisomerases. We found that most converging forks stall at a very late stage, indicating a role for additional factors. We showed that the Pif1 and Rrm3 DNA helicases promote efficient fork convergence and completion of DNA synthesis, even in the absence of type II topoisomerase. Furthermore, Rrm3 and Pif1 are also important for termination of plasmid DNA replication in vivo. These findings identify a eukaryotic pathway for DNA replication termination that is distinct from previously characterized prokaryotic mechanisms. [Display omitted] •In vitro reconstitution of the convergence of two eukaryotic replisomes•Converging replisomes stall at a late stage of DNA replication termination•The budding yeast DNA helicases Pif1 and Rrm3 stimulate fork convergence in vitro•Pif1 and Rrm3 promote fork convergence during DNA replication termination in vivo To study the mechanism of DNA replication termination, Deegan et al. reconstituted the convergence of two replisomes using purified budding yeast proteins. Surprisingly, replisome convergence is inherently inefficient but stimulated by the Pif1 and Rrm3 DNA helicases, which are also important during termination in vivo.