Abstract
The eukaryotic replisome disassembles parental chromatin at DNA replication forks, but then plays a poorly understood role in the re‐deposition of the displaced histone complexes onto nascent DNA. Here, we show that yeast DNA polymerase α contains a histone‐binding motif that is conserved in human Pol α and is specific for histones H2A and H2B. Mutation of this motif in budding yeast cells does not affect DNA synthesis, but instead abrogates gene silencing at telomeres and mating‐type loci. Similar phenotypes are produced not only by mutations that displace Pol α from the replisome, but also by mutation of the previously identified histone‐binding motif in the CMG helicase subunit Mcm2, the human orthologue of which was shown to bind to histones H3 and H4. We show that chromatin‐derived histone complexes can be bound simultaneously by Mcm2, Pol α and the histone chaperone FACT that is also a replisome component. These findings indicate that replisome assembly unites multiple histone‐binding activities, which jointly process parental histones to help preserve silent chromatin during the process of chromosome duplication.
Highlights
A subset of the many factors required to duplicate chromosomes assembles into a large and highly dynamic molecular machine called the replisome (Bell & Labib, 2016; Burgers & Kunkel, 2017; Kunkel & Burgers, 2017; Riera et al, 2017)
We show that chromatin-derived histone complexes can be bound simultaneously by Mcm2, polymerase alpha (Pol a) and the histone chaperone FACT that is a replisome component
As a more sensitive assay for impaired DNA synthesis, we combined pol1-4A with deletion of the MEC1 gene, the yeast orthologue of the ATR checkpoint kinase, which becomes essential in cells that have the slightest defect in DNA replication
Summary
A subset of the many factors required to duplicate chromosomes assembles into a large and highly dynamic molecular machine called the replisome (Bell & Labib, 2016; Burgers & Kunkel, 2017; Kunkel & Burgers, 2017; Riera et al, 2017). We show that replisome tethering of Pol a via Ctf is dispensable for efficient DNA synthesis in budding yeast cells, and instead is required to preserve epigenetic gene silencing at telomeres and the silent mating-type genes, in a manner that is dependent upon a novel histone-binding motif in the amino-terminal region of the Pol DNA polymerase subunit. These findings expand our view of the eukaryotic replication machinery and show how the coupling of a DNA polymerase to the helicase within the replisome can contribute to functions beyond DNA synthesis
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