Final answer:
DNA Polymerase I possesses exonuclease activity and is important for DNA repair, while DNA Polymerase III is an oligomeric protein essential for DNA synthesis.
Step-by-step explanation:
DNA Polymerase I is known for its role in DNA repair and it is endowed with exonuclease activity, which helps in the removal of RNA primers from the DNA during replication. Additionally, by subjecting DNA Polymerase I to mild protease treatment, it can be cleaved to form a product known as the Klenow fragment, which retains polymerization and proofreading abilities but lacks the 5'→3' exonuclease activity.
On the other hand, DNA Polymerase III is a primary enzyme involved in DNA synthesis and it is an oligomeric protein, playing a central part in the replication machinery by adding nucleotides to the growing DNA strand in a highly processive manner. DNA Polymerase III, thus, is not characterized as an endonuclease but as the main polymerase responsible for DNA synthesis.