Part of the RFC clamp loader complex which loads the PCNA sliding clamp onto DNA. The complex possesses DNA-dependent ATPase activity which is further stimulated by PCNA. Heteromultimer composed of three to four small subunits (RfcS) and one to two large subunits (RfcL). The C-terminal basic cluster region, which consists mainly of lysine residues, is important for the formation of a stable RFC-PCNA-DNA complex, although it is not critical for loading PCNA onto DNA in vitro (PubMed:16172520). An 11-mer corresponding to the PIP-box inhibits DNA synthesis by Pol I (pol). Belongs to the activator 1 small subunits family. RfcL subfamily.