Before revision:  While numerous experiments have revealed details of the molecular structure and working mechanism of DNAP , theoretical studies of the fidelity issue are still lacking. Kinetic models which considered explicitly both the polymerase pathway and the exonuclease (proofreading ) pathway were proposed since 1970s', but so far there was no rigorous treatment of such models .
After revision:  While numerous experiments have revealed details of the molecular structure and working mechanism of DNAP , theoretical studies of the fidelity issue . The first model which explicitly considered both sites was proposed in 1970s' and the basic idea was widely accepted by later models. However, all these models did not systematically and rigorously investigate the dominant factor on DNAP fidelity, i.e, the higher-order terminal effects through which the polymerization pathway and the exonuclease (proofreading ) pathway were proposed since 1970s', but so far there was no rigorous treatment of such models .