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. Subunit 2 binds ATP and single-stranded DNA (By similarity). 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.