The elongation of primed DNA templates by DNA polymerase delta and epsilon requires the action of the accessory proteins proliferating cell nuclear antigen (PCNA) and activator 1. Heteropentamer of subunits rfc1, rfc2, rfc3, rfc4 and rfc5 that forms a complex with PCNA in the presence of ATP. Belongs to the activator 1 small subunits family.