Processivity conferred by the β clamp. (a) In distributive synthesis, the Pol III core would extend a primed site by a few nucleotides and then dissociate from the DNA. It must rebind the primed site to continue synthesis. (b) Binding of a Pol III core to the β clamp tethers the core to the DNA for processive synthesis. When the Pol III core detaches from the DNA, it stays attached to the β clamp and rapidly reattaches to the DNA.