Final answer:
Positive supercoiling in the unreplicated portion of circular DNA is removed by the enzyme topoisomerase, which prevents supercoiling-induced damages to the DNA during replication.
Step-by-step explanation:
The positive supercoiling of unreplicated portion of circular DNA can be removed by enzymes known as topoisomerases. These enzymes are crucial during DNA replication as they relieve the stress caused by the unwinding of the double helix, which results in supercoiling. Specifically, topoisomerase II, also known as DNA gyrase in bacteria, performs this function by making a temporary break in the DNA's phosphate backbone, allowing the strands to be uncoiled, and then resealing the break. This action by topoisomerases helps to control the overall topology of the DNA and prevents damage that could result from excessive supercoiling. They are not part of the replisome but can act independently to address tensions in overwound DNA, essentially facilitating the smooth progression of the replication fork.