DNA replication is complex and highly regulated, and DNA replication errors can lead to human diseases such as cancer. DNA polymerase ε (polε) is a key player in DNA replication and contains a large subunit called POLE, which possesses both a DNA polymerase domain and a 3′–5′ exonuclease domain (EXO). Mutations at the EXO domain and other missense mutations on POLE with unknown significance have been detected in a variety of human cancers. Based on cancer genome databases, Meng and colleagues (pp. 74–79) previously identified several missense mutations in POPS (pol2 family-specific catalytic core peripheral subdomain), and mutations at the conserved residues of yeast Pol2 (pol2-REL)showed reduced DNA synthesis and growth. In this issue ofGenes & Development, Meng and colleagues (pp. 74–79) found unexpectedly that mutations at the EXO domain rescue the growth defects ofpol2-REL.They further discovered that EXO-mediated polymerase backtracking impedes forward movement of the enzyme when POPS is defective, revealing a novel interplay between the EXO domain and POPS of Pol2 for efficient DNA synthesis. Additional molecular insight into this interplay will likely inform the impact of cancer-associated mutations found in both the EXO domain and POPS on tumorigenesis and uncover future novel therapeutic strategies.