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

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.

ACKNOWLEDGMENTS

We are grateful to Michael Christman and members of his laboratory for strains, plasmids, and valuable advice. We thank R. D. Deshaies and G. Alexandru for comments on the manuscript and Ray Deshaies for the use of his microscope.

This work was supported by PHS GM25508. S. Edwards was supported by a PHS Research Supplement for Underrepresented Minorities.