Most DNA-dependent DNA polymerases exist as a complex with one or more noncovalently bound accessory proteins, whose presence is necessary for the correct functioning of the holoenzyme. Using the herpes simplex virus DNA polymerase as a representative member of the alpha-polymerase family, we have recreated the association between the polymerase and its accessory protein UL42 in vitro through the translation in rabbit reticulocyte lysate of bacteriophage RNA polymerase-generated transcripts encoding the two polypeptides. Study of the ability of deleted versions of the polymerase protein to bind UL42, as detected by coimmunoprecipitation of the two polypeptides, defined a carboxyl-terminal region of the DNA polymerase that was both necessary and sufficient for the association. This domain is distinct from regions of the protein previously characterized as involved in catalysis. The results suggest a strategy for the design of novel targeted antiviral drugs, which would disrupt the DNA polymerase-UL42 complex.