Role of the Putative Zinc Finger Domain of Saccharomyces cerevisiae DNA Polymerase ε in DNA Replication and the S/M Checkpoint Pathway

It has been proposed that C-terminal motifs of the catalytic subunit of budding yeast polymerase (pol) ε (POL2) couple DNA replication to the S/M checkpoint (Navas, T. A., Zheng, Z., and Elledge, S. J. (1995) Cell80, 29–39). Scanning deletion analysis of the C terminus reveals that 20 amino acid residues between two putative C-terminal zinc fingers are essential for DNA replication and for an intact S/M cell cycle checkpoint. All mutations affecting the inter-zinc finger amino acids or the zinc fingers themselves are sensitive to methylmethane sulfonate and have reduced ability to induce RNR3, showing that the mutants are defective in the transcriptional response to DNA damage as well as the cell cycle response. The mutations affect the assembly of the pol ε holoenzyme. Two-hybrid assays show that thePOL2 subunit interacts with itself, and that the replication and checkpoint mutants are specifically defective in the interaction, suggesting (but not proving) that direct or indirect dimerization may be important for the normal functions of pol ε. ThePOL2 C terminus is sufficient for interaction withDPB2, the essential and phylogenetically conserved subunit of pol ε, but not for interaction with DPB3. Neither Dpb3p nor Dpb2p homodimerizes in the two-hybrid assay.