Saccharomyces cerevisiae DNA Polymerase ε and Polymerase σ Interact Physically and Functionally, Suggesting a Role for Polymerase ε in Sister Chromatid Cohesion

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Abstract
The large subunit of Saccharomyces cerevisiae DNA polymerase ε, Pol2, comprises two essential functions. The N terminus has essential DNA polymerase activity. The C terminus is also essential, but its function is unknown. We report here that the C-terminal domain of Pol2 interacts with polymerase σ (Pol σ), a recently identified, essential nuclear nucleotidyl transferase encoded by two redundant genes, TRF4 and TRF5. This interaction is functional, since Pol σ stimulates the polymerase activity of the Pol ε holoenzyme significantly. Since Trf4 is required for sister chromatid cohesion as well as for completion of S phase and repair, the interaction suggested that Pol ε, like Pol σ, might form a link between the replication apparatus and sister chromatid cohesion and/or repair machinery. We present evidence that pol2 mutants are defective in sister chromatid cohesion. In addition, Pol2 interacts with SMC1, a subunit of the cohesin complex, and with ECO1/CTF7, required for establishing sister chromatid cohesion; and pol2 mutations act synergistically with smc1 and scc1. We also show that trf5Δ mutants, like trf4Δ mutants, are defective in DNA repair and sister chromatid cohesion.

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