DNA polymerase III holoenzyme
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- Pol III can also refer to KNM Pol III, a Norwegian guard vessel from WW2
DNA polymerase III holoenzyme is the primary enzyme complex involved in prokaryotic DNA replication. The complex has high processivity (i.e. the number of nucleotides added per binding event) and, specifically referring to the replication of the E.coli genome, works in conjunction with four other DNA polymerases (Pol I, Pol II, Pol IV, and Pol V). Being the primary holoenzyme involved in replication activity, the DNA Pol III holoenzyme also has proofreading capabilities that correct replication mistakes by means of exonuclease activity working 3'->5'. DNA Pol III is a component of the replisome, which is located at the replication fork.
The replisome is composed of the following:
- 2 DNA Pol III enzymes, made up of α, ε and θ subunits.
- the α subunit has polymerization activity.
- the ε subunit has proofreading activity.
- 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 connect the 2 DNA Pol III enzymes.
- 1 γ unit which acts as a clamp loader for the lagging strand Okazaki fragments, helping the two β subunits to form a unit and bind to DNA. The γ unit is made up of 5 γ subunits.
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