*the θ subunit stimulates the ε subunit's proofreading.
2 β units which act as sliding DNA clamps, they keep the polymerase bound to the DNA.
2 τ units which act to dimerize two of the core enzymes.
1 γ unit which acts as a clamp loader for the lagging strandOkazaki fragments, helping the two β subunits to form a unit and bind to DNA. The γ unit is made up of 5 γ subunits which include 3 γ subunits, 1 δ subunit, and 1 δ' subunit. The δ is involved in copying of the lagging strand.
DNA polymerase III synthesizes base pairs at a rate of around 1000 nucleotides per second. DNA Pol III activity begins after strand separation at the origin of replication. Because DNA synthesis cannot start de novo, an RNA primer, complementary to part of the single-stranded DNA, is synthesized by primase : --------> * * * * ! ! ! ! _ _ _ _ _ _ _ _ | RNA | <--ribose -phosphate backbone G U A U | Pol | <--RNA primer * * * * |_ _ _ _| <--hydrogen bonding C A T A G C A T C C <--template ssDNA _ _ _ _ _ _ _ _ _ _ <--deoxyribose -phosphate backbone $ $ $ $ $ $ $ $ $ $
Addition onto 3'OH
As replication progresses and the replisome moves forward, DNA polymerase III arrives at the RNA primer and begins replicating the DNA, adding onto the 3'OH of the primer: * * * * ! ! ! ! _ _ _ _ _ _ _ _ | DNA | <--deoxyribose -phosphate backbone G U A U | Pol | <--RNA primer * * * * |_III_ _| <--hydrogen bonding C A T A G C A T C C <--template ssDNA _ _ _ _ _ _ _ _ _ _ <--deoxyribose -phosphate backbone $ $ $ $ $ $ $ $ $ $
Synthesis of DNA
DNA polymerase III will then synthesize a continuous or discontinuous strand of DNA, depending if this is occurring on the leading or lagging strand of the DNA. DNA polymerase III has a high processivity and therefore, synthesizes DNA very quickly. This high processivity is due in part to the β-clamps that "hold" onto the DNA strands. -----------> * * * * ! ! ! ! $ $ $ $ $ $ _ _ _ _ _ _ _ _ _ _ _ _ _ _| DNA | <--deoxyribose -phosphate backbone G U A U C G T A G G| Pol | <--RNA primer * * * * * * * * * *|_III_ _| <--hydrogen bonding C A T A G C A T C C <--template ssDNA _ _ _ _ _ _ _ _ _ _ <--deoxyribose -phosphate backbone $ $ $ $ $ $ $ $ $ $
Removal of primer
After replication of the desired region, the RNA primer is removed by DNA polymerase I via the process of nick translation. The removal of the RNA primer allows DNA ligase to ligate the DNA-DNA nick between the new fragment and the previous strand. DNA polymerase I & III, along with many other enzymes are all required for the high fidelity, high-processivity of DNA replication.
