Function of three polymerases during the Okazaki fragment cycle. Two Pol III cores are attached to β clamps on the leading and lagging strands, creating a loop. Primase binds to DnaB helicase and synthesizes an RNA primer (purple). The clamp loader assembles a β clamp onto the new RNA primer. The second lagging-strand Pol III core (third polymerase) assembles with the new clamp while the first lagging-strand Pol III core is extending an Okazaki fragment, creating two DNA loops. The first lagging-strand Pol III core ejects from the β clamp on the first Okazaki fragment, leaving the clamp on the DNA.