Proliferating cell nuclear antigen can interact with DNA polymerase epsilon on linear DNA templates, even in the absence of other auxiliary factors (replication factor C, replication protein A), and thereby stimulate its primer recognition and DNA synthesis. Using four characterized mutants of proliferating cell nuclear antigen containing three or four alanine residue substitutions on the C-terminal side and the back side of the trimer, we have tested the kinetics of primer binding and nucleotide incorporation by DNA polymerase epsilon in different assays. In contrast with what has been found in interaction studies between DNA polymerase delta and proliferating cell nuclear antigen, our data suggested that stimulation of DNA polymerase epsilon primer binding involves interactions with both the C-terminal side and the back side of proliferating cell nuclear antigen. However, for stimulation of DNA polymerase epsilon DNA synthesis, exclusively the C-terminal side appears to be sufficient. The significance of this dual interaction is discussed with reference to the physiological roles of DNA polymerase epsilon and its interaction with the clamp proliferating cell nuclear antigen.