The architecture of a eukaryotic replisome

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• The eukaryotic DNA replication fork is a complex machinery responsible for duplicating the genome.
• The canonical model places the CMG helicase at the fork's forefront, unwinding DNA, with polymerases trailing behind.

Purpose of the Study:

• To directly visualize the Saccharomyces cerevisiae replisome architecture using single-particle electron microscopy.
• To resolve the spatial arrangement of key replication proteins at the eukaryotic DNA replication fork.

Main Methods:

• Single-particle electron microscopy (EM) of Saccharomyces cerevisiae replisomes.
• Structural analysis to determine protein positioning within the replisome.

Main Results:

• Contrary to established models, the leading-strand polymerase epsilon (Pol ɛ) was found positioned ahead of the CMG helicase.
• Ctf4 and the lagging-strand polymerase alpha-primase were located behind the CMG helicase.
• Leading-strand DNA must thread through the Mcm2-7 ring and U-turn before reaching Pol ɛ.

Conclusions:

• The eukaryotic replisome exhibits an unexpected configuration, with Pol ɛ preceding the CMG helicase.
• This architecture suggests a novel mechanism for leading-strand DNA synthesis and processing.
• Provides a structural basis for future replisome mechanism and regulation studies.