Forms the sliding-clamp-loader together with the small subunit (PubMed:10585481). The clamp loader holds the clamp in an open conformation and places it onto the DNA (PubMed:22194570). The sliding-clamp-loader consists of 4 large subunits and 1 small subunit (PubMed:2663867, PubMed:10585481). Interacts with the sliding clamp; this interaction allows the sliding-clamp-loader to open the sliding clamp (PubMed:22194570). Part of the replicase complex that includes the DNA polymerase, the polymerase clamp, the clamp loader complex, the single-stranded DNA binding protein, the primase, the helicase and the helicase assembly factor (PubMed:16800624). Belongs to the Tevenvirinae sliding-clamp-loader small subunit family.