The present invention is to construct a DNA replication reaction system which is excellent in versatility and is easily used. An amino acid sequence of a PCNA monomer which is one of factors involved in DNA replication is prepared so that amino acid residues causing mutual charge repulsion constitute a site which causes, when an N terminal region of the PCNA monomer and a C. terminal region of another PCNA monomer act as an interface to form a multimeric complex, an intermolecular interaction of the monomers in an interface region of the monomers.
