List and describe the function of the ten subunits constituting DNA polymerase III. Distinguish between the holoenzyme and the core enzyme.

Key Concepts

DNA Polymerase III Structure

DNA Polymerase III is a multi-subunit enzyme essential for DNA replication in prokaryotes. It consists of ten subunits, including the core enzyme made up of three main components: alpha (α), epsilon (ε), and theta (θ), which are responsible for polymerization and proofreading. The additional subunits, such as the clamp loader and sliding clamp, enhance the enzyme's processivity and stability during DNA synthesis.

Holoenzyme vs. Core Enzyme

The holoenzyme of DNA Polymerase III refers to the complete functional form that includes the core enzyme along with additional subunits necessary for its full activity, such as the clamp loader complex. In contrast, the core enzyme consists solely of the essential polymerase components (α, ε, θ) and lacks the accessory factors that facilitate high processivity and efficient DNA replication.

Function of DNA Polymerase III Subunits

Each subunit of DNA Polymerase III plays a specific role in DNA replication. The alpha subunit is responsible for the polymerization of nucleotides, the epsilon subunit provides proofreading activity to correct errors, and the theta subunit stabilizes the epsilon subunit. Other subunits, like the beta clamp, encircle the DNA, allowing the polymerase to remain attached during replication, significantly increasing the enzyme's efficiency.