Schizosaccharomyces pombe Cells Lacking the Amino-Terminal Catalytic Domains of DNA Polymerase Epsilon Are Viable but Require the DNA Damage Checkpoint Control

Abstract

ABSTRACT In Schizosaccharomyces pombe , the catalytic subunit of DNA polymerase epsilon (Pol ɛ) is encoded by cdc20 + and is essential for chromosomal DNA replication. Here we demonstrate that the N-terminal half of Pol ɛ that includes the highly conserved polymerase and exonuclease domains is dispensable for cell viability, similar to observations made with regard to Saccharomyces cerevisiae . However, unlike budding yeast, we find that fission yeast cells lacking the N terminus of Pol ɛ ( cdc20 Δ N-term ) are hypersensitive to DNA-damaging agents and have a cell cycle delay. Moreover, the viability of cdc20 Δ N-term cells is dependent on expression of rad3 + , hus1 + , and chk1 + , three genes essential for the DNA damage checkpoint control. These data suggest that in the absence of the N terminus of Pol ɛ, cells accumulate DNA damage that must be repaired prior to mitosis. Our observation that S phase occurs more slowly for cdc20 Δ N-term cells suggests that DNA damage might result from defects in DNA synthesis. We hypothesize that the C-terminal half of Pol ɛ is required for assembly of the replicative complex at the onset of S phase. This unique and essential function of the C terminus is preserved in the absence of the N-terminal catalytic domains, suggesting that the C terminus can interact with and recruit other DNA polymerases to the site of initiation.