E. coli replisome structure

Replisome is a multiple protein complex that works together on the template in order to synthesize new DNA. Basically,  E. coli replisome contains a hexamer helicase, single stranded binding protein SSB, primase DnaG, 2 Polymerase III core, a gamma complex (also known as clamp loader) and β clamp. Helicase is a homohexamer that encircles the lagging strand like a ring. It translocates along the ssDNA and separate the duplex DNA using energy from ATP hydrolysis. The unwinding of double stranded DNA and discontinuous synthesis of lagging strand leaves Continue Reading →

Why DNA Polymerase III Holoenzyme can synthesize DNA with very high processivity?

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 Continue Reading →