Final answer:
DNA polymerase III in prokaryotes has multiple subunits, including a unique clamp loader complex. This complex is responsible for loading the sliding clamp onto DNA, and each component of the clamp loader complex is found only once in Pol 3.
Step-by-step explanation:
In prokaryotes, DNA polymerase III (Pol 3) is responsible for the bulk of DNA synthesis during replication. It is a multi-subunit enzyme composed of several different polypeptide chains. Among these subunits, is the clamp loader complex that contains components found only once in Pol 3. Specifically, the clamp loader is responsible for loading the sliding clamp (also called the β clamp) onto the DNA. The clamp itself is a dimer made up of two identical β subunits, and it encircles the DNA, keeping the polymerase firmly attached to the template strand. This allows Pol 3 to synthesize DNA processively, meaning it can add nucleotides rapidly without releasing the DNA strand.
Based on the information provided, there may be confusion due to differing representations of the subunits in the question. In reality, the Pol 3 core enzyme in prokaryotes such as E. coli is composed of several subunits: two α (alpha) subunits, one each of ε (epsilon) and θ (theta), along with the β sliding clamp, which comes in pairs. The α subunit is responsible for the polymerase activity, the ε subunit functions as the 3'↓5' exonuclease for proofreading, and the θ subunit supports the ε subunit's proofreading function.