Models explaining results on the genetic interaction of mutants with defects in the active site and proofreading of DNA polymerase ε. Thickness of arrows indicates the relative probability of a depicted pathway. See text for explanations. (A) Dissociation-proofreading. The newly synthesized DNA is in red. 'M' stands for incorrectly inserted nucleotide. DNA polymerase is drawn as octagonal oval; an exonuclease is drawn as rectangle. (B) Three distinct roles of Pol ε in replication.