While Polymerase III core with the polymerase activity resides on the α subunit can only synthesize DNA with 10–20 nucleotides per binding event, replicative DNA synthesis by pol III holoenzyme is highly processive. This rapid increment in processivity of Pol III Holoenzyme is enhanced by β subunit. The β subunit is a doughnut-shaped dimer that can form a ring around DNA and functions as a sliding clamp that inhibits dissociation of pol III core from DNA during chain elongation. By this, Pol III Holoenzyme can synthesize more than 5 kb per binding event. The loading of β clamp onto the primed-DNA is controlled by γ complex that contains five subunits (gamma, delta, delta prime, chi and psi).