A Ctf4 trimer couples the CMG helicase to DNA polymerase alpha in the eukaryotic replisome

作者：Simon Aline C; Zhou Jin C; Perera Rajika L; van Deursen Frederick; Evrin Cecile; Ivanova Marina E; Kilkenny Mairi L; Renault Ludovic; Kjaer Svend; Matak Vinkovic Dijana; Labib Karim; Costa Alessandro; Pellegrini Luca^*

来源：Nature, 2014, 510(7504): 293-+.

DOI：10.1038/nature13234

Efficient duplication of the genome requires the concerted action of helicase and DNA polymerases at replication forks(1) to avoid stalling of the replication machinery and consequent genomic instability(2-4). In eukaryotes, the physical coupling between helicase and DNA polymerases remains poorly understood. Here we define the molecular mechanism by which the yeast Ctf4 protein links the Cdc45-MCM-GINS(CMG) DNA helicase to DNA polymerase alpha (Pol alpha) within the replisome. We use X-ray crystallography and electron microscopy to show that Ctf4 self-associates in a constitutive disk-shaped trimer. Trimerization depends on a beta-propeller domain in the carboxy-terminal half of the protein, which is fused to a helical extension that protrudes from one face of the trimeric disk. Critically, Pol alpha and the CMG helicase share a common mechanism of interaction with Ctf4. We show that the amino-terminal tails of the catalytic subunit of Pol alpha and the Sld5 subunit of GINS contain a conserved Ctf4-binding motif that docks onto the exposed helical extension of a Ctf4 protomer within the trimer. Accordingly, we demonstrate that one Ctf4 trimer can support binding of up to three partner proteins, including the simultaneous association with both Pol a and GINS. Our findings indicate that Ctf4 can couple two molecules of Pol alpha to one CMG helicase within the replisome, providing a new model for lagging-strand synthesis in eukaryotes that resembles the emerging model for the simpler replisome of Escherichia coli(5-8). The ability of Ctf4 to act as a platform for multivalent interactions illustrates a mechanism for the concurrent recruitment of factors that act together at the fork.

• 出版日期2014-6-12