Recombination and Pol ζ Rescue Defective DNA Replication upon Impaired CMG Helicase-Pol ε Interaction

The CMG complex (Cdc45, Mcm2-7, GINS (Psf1, 2, 3, and Sld5)) is crucial for both DNA replication initiation and fork progression. The CMG helicase interaction with the leading strand DNA polymerase epsilon (Pol epsilon) is essential for the preferential loading of Pol epsilon onto the leading strand, the stimulation of the polymerase, and the modulation of helicase activity. Here, we analyze the consequences of impaired interaction between Pol epsilon and GINS in Saccharomyces cerevisiae cells with the psf1-100 mutation. This significantly affects DNA replication activity measured in vitro, while in vivo, the psf1-100 mutation reduces replication fidelity by increasing slippage of Pol epsilon, which manifests as an elevated number of frameshifts. It also increases the occurrence of single-stranded DNA (ssDNA) gaps and the demand for homologous recombination. The psf1-100 mutant shows elevated recombination rates and synthetic lethality with rad52 Delta. Additionally, we observe increased participation of DNA polymerase zeta (Pol zeta) in DNA synthesis. We conclude that the impaired interaction between GINS and Pol epsilon requires enhanced involvement of error-prone Pol zeta, and increased participation of recombination as a rescue mechanism for recovery of impaired replication forks.